My video camera has a terrible mike and I've found that applying a lot of compression can help, but only after applying other effects, such as high pass filters to get rid of the rumble. Why not just apply compression straight up? because every consumer video camera on the market has a built-in automatic gain control which is similar but better because it works at the source to prevent distortion. Of course, most of my videos are stupid, and a lot of some videos on youtube are really cool. Especially some of the music related ones. The last thing you want with a music related video is someone mucking with the sound, right? Well, that's what youtube has started to do according to niceone on slashdot, but he also offers a nice suggestion for getting rid of the problem by tricking the the youtube compressors. Haven't tried it yet, but thanks for the warning niceone!
There are some example clips and so on on his post and I could hear the difference even on my built-in MacBook speakers, which are the worst.