A couple weeks ago I asked the question about how long a video the D5000 could make. I got several good answers (but to be honest I don't remember what they were).
Today, I had the opportunity to make a couple videos and I learned that the apparent limit is 20 minutes. I had put in a 4GB SD just to make sure the size of the media didn't limit the video recording time. The first I made started at 20 minutes and counted down to about 5 before I stopped it. A little while later I started another and it again started at 20 minutes again. I let it run about 5 minutes and shut it off. Finally I started a 3rd video just to see if it would start at 20 minutes again. It did. I'm quite pleased with this performance, especially since it means you could stop a video and immediately restart it and make a much longer film.