For the first time since LFR came out I encountered another multiboxer in LFR a few days ago. I've been running LFR almost every week since it came out with multiple teams and people comment on it in almost every group (when they notice, most of my characters have different names/classes and transmogs so they don't look like typical multibox teams), so I'm guessing PvE multiboxers are incredibly rare.

If I had 10 accounts I'd definitely try soloing raids, at least the easier bosses. Would be fun. I've currently got 3 and now with WoW tokens I'm almost tempted to get another two accounts for heroics and challenge modes, but I'm not sure if I could handle tanking and healing at the same time.