Not really sure, but I assume I'll do a mix of both. I'll definitely do the content solo on at least one shaman and hunter, because I like playing those classes solo. After that I'm sure I'll level a few teams to 85. My priest + 4 mages are still 60 (broken wrist, canceled my subs for a while) and I would like to level through the new 1-60 content with at least one group.

I have friends that will buy Cata and I expect to play with them. As fewer and fewer friends play WOW, there's less reason for me to want to play. I multibox because it's fun, but it's not as much fun as playing with my friends and it is not enough by itself to keep me playing.