I had the same experience, after struggling with slow buffering on YouTube I started to search for any answers.. The easy-to-go solution with blocking IP's did not work and I didn't want to use any lightweight YouTube clients either.
So I got a Trial Hotspot Elite subscription to test it since one of the pointers I got from Google was that a proxy/VPN could help.. And indeed it did. YouTube is a dream now, I have no problem by streaming 1080p anymore, both on my PC and my mobile phone. So it took me about 2 minutes (had to test many videos..) before I decided to buy 1 year subscription with the code from Linus.
For reference to other users: I'm located in Norway (Oslo) and Telenor is my ISP.