Most of them do work. The only problem I have seen is that everything is so stretched out on a tablet it doesn't look good. But the app still works. There are a few apps that are built strictly for one or the other. But for the most part those will not show up in the Market if you are on the wrong device, or it will state in the description that it may, or may not, work. The biggest problem I have seen is that say an app is built for Honeycomb won't even load on another version. Download it and try it, can't hurt. If it is a paid app then get it through the Market. They have a 24 hour refund policy. Good look.