Tarmack
Rhetorical Porcupine
Most large networks have a good sized hub channel that can act as a promotion tool. The problem is that most YouTubers content sucks and isn't worth the network tarnishing it's hub reputation by uploading.
There is additional promotion that YouTube does for partners. It is debatable how much more over and above Adsense, but it certainly is there (hit up Analytics and look for "YouTube Partner Promotion" in traffic sources).
There is also debate on whether partnership is one of the factors in the organic search rank. Indications suggest this is true however YouTube would of course never confirm it.
There is additional promotion that YouTube does for partners. It is debatable how much more over and above Adsense, but it certainly is there (hit up Analytics and look for "YouTube Partner Promotion" in traffic sources).
There is also debate on whether partnership is one of the factors in the organic search rank. Indications suggest this is true however YouTube would of course never confirm it.