I've noticed that I play fewer hours when multiboxing, but I actually get more done.

I can run into instances without spending 30minutes to an hour looking for people. Being able to heal and rez yourself is a HUGE deal. If I lose one of the toons, it's not a catastrophe. Heck, it isn't a big deal to wipe either. Just run one guy back and have him rez everyone else.

My 5 shaman are now level 28 and I just did Stockades last nite. Was pretty cool to run around and blast everything. Yup, I died a bunch because my fire totems aggroed 6 guys, but i still had fun.