...it's perfect for that. Use the water busus to get to the other areas, and you can get one the entire length of the grand canal, which is fabulous.
Buy a decent guide book and stick by the recommendations in that, restaurat wise. That maxim has never let us down. .
Naranzaria is very nice (Rialto Bridge) and there's an authentic italian place at the Arsenale (with all the lion statues outside).
Rule #1 when we travel is "Never eat at a place that has pictures of the food outside".
Get over to Burano on the water bus for an unspoilt litle jaunt, some great seafood places there.
Murano, with all the glass, is a bit tourist trap-y.
The "secret itinerary" tour of the Doge's Palace is well worth it , but you must pre book.

It's a wonderful place.

Literally. Just wander about and be amazed by the place. You can do the main tourist sites in a day (the Doge's Palace, San Marco and so on) leaving the rest of the time for slow wanders. You probably won't know where you are most of the time, but so long as you know which side of the Grand Canal you're on you won't got too lost.

Take a long trip out to Torcello, cross the Grand Canal by Traghetto (stand up on the crossing unless you want to stand out as a tourist), stop frequently for a coffee or a glass of wine (un ombra).

I'm no foody, and happy with pizza and pasta, so can't really help on the restaurants though I loved Campo Santa Margherita in the University district for a range of places off the usual tourist track.

PS - And watch Francesco da Mosto's BBC Venice series before you go!

We were there in April and had a lovely time.

- as above, wandering around aimlessly is the best plan - you'll get repeatedly lost, but only temporarily as you'll soon pop out onto a square or by a canal where you can regain your bearings.
- using the traghettos (traghetti?)to cross the grand canal is a cheap way to have a gondola ride.
- the Peggy Guggenheim Gallery would be my recommendation if you're going to 'do some art'.
- the Church of San Giorgio Maggiore has, I think, a better view from its campanile than the S Marco one and is much quieter.
- if you can stretch your budget to it, arriving by water taxi is a wonderful way to enter the city.
- food - there are some good recommendations on the Guardian website - there is one from January 2009 on budget eats that we used and all were fine.

got lost and found it to be hellishly expensive (but then I was a student). Obvious advice, but it is a city to wander about in, believe the opera house which was damaged by fire has re-opened and is supposed to be beautiful. I would also take the opportunity to go and see some of Palladio's villas nearby. They are not open all the time and it might be logistically difficult but do make enquiries. Before you g, read Jan Morris's book on the city. Enjoy the trip.

to say all that. All good advice. I've been there about a dozen times, and can still do some of the walks in my head. The only advice I'd add is to take comfortable walking shoes, and not to expect too much excellence in the culinary department. Compared to just about any other Italian city, the food is a disappointment. I'd avoid the Guggenheim, too. No real sense of being in Venice there. And I'd definitely shell out for coffe and cakes at Florian's while there's a string quartet playing. It costs a little more than Starbucks, but it's a major, major thrill.

San Giovanni di Paulo and the Frari are both must-sees - immense and scary brick cathedrals. Canova's tomb still gives me Lovecraftian chills.

and can't wait...mind you on the previous 2 occasions the Pope dies so beware Pope Benedict...we're there next October.

Venice is a nice place to "be" in. Just wander around and enjoy it. Every church has a Titain or a Venerase, whom the art teacher GLW tells me are quite good. Do the "upstairs" but of St Marks. It's pretty damn good. The secret itinery tour bobness mentions is supposedly good and I believe you can book online before going. We didn't and couldn't do it.

As for food. Avoid Florians and Harry's bar and anywhere on the waterfront near the Doge's Palace. Basically the further away from St Marks square the cheaper and better it gets. We found some good ones near the Fish Market by the Rialto Bridge and a couple near Arsenale and the football stadium. We tended to eat in restaurants at lunchtime and let hit some of the little bars for a drink and a calzone or two or three. Venice is great for snacking. There's some reasonable and cheap places bar/restaurants across the Grand Canal from St Marks. Get a traghetto (I sat..locals stand) or walk over the wooden bridge - I forget the name but you'll know the one when you get there.

Enjoy.

All expensive, and often for decidedly average food.

This was the best for quality & value:

http://www.tavernasanlio.com/restaurant.htm

also - visit the Cimitero di San Michele (the cemetary island) which is a stop off the waterbus on the way to murano island - very peaceful, a bit like pere lechaise in paris.

We also went to the Lido beach, which in november was unusually warm and walked about a bit.
Dont go up the tower in st marks, way too expensive for what it is!

as for restaurants, plenty to go at, just look for the ones that look like its ful of locals/families, as these are invariably the best ones, especially off the main touristy areas.

you'll get lost, even with a map! I stood up on the traghetto, jeez what a frightner!

Also theres a waterbus service that goes round the whole grand canal/island, which a great cheap way to spend an hour or so and see more for a few euros!

eFrari
The Arsenal
One or more of the islands
Dorsoduro
If you're coming from the airport take a water taxi - its expensive but magical
Food is important to keep you alive but don't worry too much about the Perfect Meal its the place that matters
Have Sex

I didn't know there was a St Marks Piazza in Bangkok..... oh that floating city......

Water buses are very expensive for single trips, but come down in price to only quite expensive if you buy multi-day travelcards; doing that also means that instead of using them simply to get from A to B, you can jump on and off to do some random exploration whenever you feel like it (and sit down while you do it, especially good if you've been doing a lot of walking, which is always likely in Venice). You can also visit outlying parts of the lagoon, or cruise the length of the Grand Canal, either of which would require Russian oligarch levels of wealth if you fancied doing them in a water taxi or gondola.

Disclaimer: Venice is unique and it knows it. The concept of what consitutes good value, in transport and everything else, is somewhat different to anywhere else...

and otherworldly. So magical and otherworldly, in fact, that I proposed to my wife there (after 16 years of blissful cohabitation with no desire to tie the knot.) She said yes and we spent the balmy summer evening walking around St Marks listening to the various orchestras playing in the square, tearful at the sheer unexpectedness and magnificence of it all. Woke up the next morning saying to each other: Did that really happen? Thankfully, it did!

my schedule for the four days is looking pretty full.

Thought I might give this a bump for any late suggestions.

Also, has anyone been to the Teatro La Fenice?