I don't know if this is a tip or a trick, but whatever:
I had an issue this morning while searching through the Mabilo Ringtone app. Basically, everything went black except for the notification bar. I was able to back out of the app, and when I went back, it wouldn't search. I had considered maybe reinstalling the app, so I went to the Market and I couldn't pull anything up. Went back to the Home screen and just hit an app (Maps). That wasn't working right, either.
So, I shut off my WiFi and switched to 3G. Everything was back to normal. I'm now back on WiFi and there's no issue. Sometimes I think there's just too much going on and things need to reset themselves.
So if you encounter a similar issue, give that a try.