I have been monitoring my visitors screen resolutions for a while and have noticed that 1024x768 has dropped to 8% of my visits lately. Being the narrowest screen resolution I receive, i'm keen to drop it as soon as possible and start using a fixed size that is larger.
When would you suggest dropping support for smaller screen resolutions? Do you think sub 10% is good enough?
I'd say never.
Take a look at the Responsive Web Design approach to it:
http://coding.smashingmagazine.com/2011/01/12/guidelines-for-responsive-web-design/
http://www.alistapart.com/articles/responsive-web-design/
Why phase out support for a screen resolution (and lose 8% of your audience, or more, with mobile and all) when you can just rearrange your items to fit and keep them? You can have your base design as large as you want, just don't forget the less fortunate... :)