I've been 10-boxing in Cata since its release. However, I think you are asking about someone soloing 10-man raids, which I have not done. I've killed almost every boss in the raid content (all but the last three in TotFW, BwD, and BoT) multiple times while playing solo and I'm hard pressed to think that someone could 10-box that content. There are simply too many things going on at once and a lot of coordinated movement in the fights that is extremely punishing if you don't get it exactly right.

I do think soloing 10-man BH would be possible. Magmaw *might* be, but would be very difficult. I haven't put in the time to try these out b/c I'm having too much fun with other guildies 5- or 6-boxing BH and solo running the other raid bosses with other friends. We plan on running 25M BH this week and I'll probably be 10-boxing that. All in all, I'm definitely happy I've kept the 10 accounts going, but haven't soloed anything.