My feeling is that - as with 800x600 - I will likely stick with 1024x768 as the baseline for a little longer than I should... Just to be sure. A site that takes up a bit to little room is less annoying that a site that takes up too much, IMO.
See here for a somewhat old but useful discussion on the topic: http://www.cameronmoll.com/archives/001220.html
Then yeah, there's the whole fluid width angle too... Most of the sites I have designed are actually fluid width (useable at 800x600 and up) rather than fixed. Fixed width is something that I have only more recently started experimenting with.
If there's no reason to exclude people though, then you may as well include as many as you can. Older browsers (IE6 anyone?) can be cut on newer things as well if the time to test and ensure it works in them isn't worth it, but that depends on your audience again.
Then there's the accessibility question. You're not developing for users within public or govt institutions are you? ;)
Thank the laptop/LCD boom for that.
I mockup up all my designs at 1000 pixels wide.
And since this is a flash app, it HAS to all fit!
For my gaming sites, less than 1% of our visitors use 800x600 or lower.
We'd probably go with 1024 in the future for all our sites if we have a compelling design that needs it.
Just remember that really wide text is hard to read, and break it down into a readable column width for text, plus other elements.
P.S. yes, peple have larger screens, but it does not mean they maximize the browser window. It's especially true of Mac users.
What does everyone here think of creating a separate .mobi type site versus taking the time to make your regular site "mobile-friendly"?