How many tables can/should you play?
 

Since I am mainly a low-limit player, I like to play multiple tables at once (usually 4). This serves 2 purposes - to increase my overall profit per hour and lower my relative risk. If you play 4 tables of $1/$2, you will have a lower variance than playing 1 table of $4/$8.

Since low-limit games are very mechanical, there is not as much need to read individual players so I don't have to pay attention to any 1 table for too long. It also helps keep my disciplined because if I only play 1 table and I get crappy hands for an hour straight I will be so bored that I will play a marginal hand when I shouldn't.

Question: How many tables at once do you play? What are the advantages and disadvantages?