No, you don't really need more than 8 MP. I think my cameras take 10MP and 12MP, respectively...but since I end up resizing them for the computer anyway, I actually just set my cameras to take 5MP pictures. The file sizes are a bit smaller that way, so I can store more on the SD card before having to download them. This is usually only a concern if I go on a vacation for a week and can't download the pictures for awhile.
The cool thing about high res cameras, though, is that if you take a picture at the full resolution, and the object of interest is some distance away (say, an eagle flying or a bear on the opposite side of a river), you can crop the picture down pretty small and still have a very good quality image.