I started two boxing back in daoc when everyone and their mother had a buffbot so i had one too (shame on me... i know)
In wow I was actually one boxing for quite some time playing a rogue in a raiding guild. When BC came out it was fun at first doing the 5mans but after a while we started working on kara and thats what it was: "work".
Many things came together that made me stop playing my rogue: Rogues were not wanted very much in raids, we didn't dps as good as we used to, playing a rogue is incredibly boring and our raid leader (a mage) was sure he knew better how to equip and play a rogue than I did.
At first i considered rerolling a warrior because i have always liked the responsibilities warriors have in a raid but there simply were too many tanks in our guild so i stopped playing at all. Aftrer a month of not playing lotro came out so i started dual boxing that but the game somehow didn't "feel" right - I think it is the fact that you push a button and sometimes the char does the assigned action later, sometimes not at all.. i don't know, it is a nice game but just not for me.
After a week or two not playing at all i decided to 5box - i had that thought a couple of months back but was scared of the money i had to invest (I needed 2 complete systems and one monitor). After contemplating for a couple of days i just went to my local dealer, got the hardware and started playing my now lvl 47 group.
Why do i do it?
* Because oneboxing (especially a class like a rogue) is boring
* Because it is something not everybody does - i think it is interesting how people react (yesterday someone posted a ticked because he saw my toons all in the same guild and named almost the same just standing in UC). I have had alliance guys spit on me and other log to a horde alt to tell me how cool they think it is what i do.
* I want to see how far i can get: can i do all the 5 mans in BC? is it possible to do heroics? How about old stuff like ubrs and ZG? Just wanting to find out what is possible.
* And most improtantly: Why does a dog lick his balls? Because he can!

Bunny