I do a lot of FRAPS editing stuffs and when I wrap them up for youtube, I ususally go in Premiere Export for the 5.1 level and boost the VBR to nearly max, and let Youtube handle the rest. I mostly used these level of bitrates because I don't have a good idea of what they do, so to comfort me I used the best quality possible.

But I try to narrow down the unnecessary bits and lower the file size. Any recommendation for a bitrate to an acceptable HD quality for Youtube and Vimeo?

On a side note, I also noticed my settings were unusable even on computer level, Windows Media Player have problems playing those high bitrate files and so is VLC. If I use Level 4.1 it start to be fine, but WMP start having artifacts (none observed in VLC).