I think I though this was going to be cool before I could get it, but I have to say it’s not really something I care too much about. I’ve stopped posting my own videos to YouTube (I’m all about Viddler now) and really only check the site when I get a link from someone. The mobile experience is pretty limited – no way to search for a vid, or open a link from an email — let alone keep tabs on your subscriptions.
If you are interested however, set your mobile to http://m.youtube.com. Be sure that your Real Player has an AP set – WiFi works best.
BTW – This has actually worked for a while on the N95 in the Video Centre application.