The short answer is yes, 800 is dead.
The long answer is that it depends on the demographic of your users. The majority of your users will have a screen width of 1024 or more. The question is how many do not, and how many becomes significant for you. For example at clicktale.com, 90% of the page views are viewed with a resolution of 1024 or more. On the other hand, at codebuildingblocks.com, only 80% of the page views are viewed with a resolution of 1024 or more.
I would suggest that you monitor your site with a web-analytics service that is able to collect screen resolution data (most do) and decide for yourself.
Based on the data that we collect at clicktale.com (some variation of a novel web analytics service) I can say that, on average, 77% of page views are viewed with a resolution of 1024 or more.
Arik.