Still having the issue today, very intermittent though, but generally not good.
On the flip side, I can easily and efficiently stream Vimeo HD (which is higher bandwidth than Youtube I believe). It's definitely a Youtube issue, just not sure why not everybody is affected.
I use multiple platforms, so it's not a cookie issue or anything, and reset my 2Wire and router, so it's not anything related to my IP address afaik
(since that would change anyway).
I ran the Youtube speedtest and noticed it averaged about 4000 kbps, not bad, but not nearly what it should be (their graph shows that I used to be up around 11000 kbps a week or two ago), but it will often drop to MUCH lower levels as seen here.
I called MTS support and they didn't have any answers. They told me to try a different browser, hardwire connection, etc, but I've done all that (and tried my iTouch) and only Youtube is affected.