I am fairly new to the devices, service, and selling them... The "official" literature I have, as well what I was told by the BB rep when we did our 2 day training, and later by another BB rep when he did my in store setup run through, was that no streaming video at the time, ie youtube, but they were hoping to get it added in soon, like when they launched the Bold/Storm, but that you would have to have one of those devices...
Well, of course I am not one to just take what someone says, so the second I got my 8110, I went straight to youtube and tried to play a video, no go... not shocked, but disappointed, and from my little experimentation, no way to download the video ei...
What I found through experience is that m.youtube.com will stream, but you need to have an APN entered in the TCP settings... except some carriers you don't because one of the BB books has these settings emulated in it.
I also found that you can't download from m.youtube.com, so if you want to save it to your phone, check out vuclips.com
That site is supposed to allow streaming too, but I have yet to get it to with my 8110, although a friend of mine with a 8130 was able to get it to stream, I think it has to do with the fact he is running on 3g with Sprint.