I started playing 2 tables a couple of weeks ago ($5 SnG 9 man) and really struggled even with a 32" monitor. Had a couple of weeks when I couldn't play and came back to it more relaxed and prepared and found it much better than one table (not quite Multitabling I know!!!)
I am very much a learner so can still do the maths, get some reads, etc but also not get bored as so many have mentioned. It has really helped my learning by allowing me to play enough
hands to test focus areas and plays.
Furthermore, it has reduced my frustration - I'm not particularly tilty anyway but when you have the empty void once your AA has been cracked you have that empty void if nothing else going on, whereas if you have another game running, its a distraction and you tell yourself to focus as there is work to do. I guess you could argue you might go on tilt and smash that one in too!
For what it is worth I've been playing 1 reg and 1 turbo at the same time - seems to balance the amount of action suitably and allow me to practise the various stages of play.