I will play up to 4 tables at the same time. Usually I am watching all 4 tables because I am waiting for some decent cards. The problem you can run into is hitting hands on all the tables at the same time and you need to be able to go from one table to the next very quickly, remembering who bet what from which position, decide whether to fold/call/raise, count your outs and calculate
odds all within a couple seconds before the other tables you are at time out.
The benefit to multi tabling (besides seeing more hands/hr) is that you need to play a bit more selectively. If you are the type to become a bit impatient waiting for top 10 or top 15 hands or playing proper positional poker, multi tabling will probably keep you a bit more interested since there is more to watch and not enough time to play junk hands. There is a better chance of making more money, but now there is a better chance of losing more money as well. The more tables you play, the bigger the swing you can have in either direction. If you are not skilled enough to play multiple tables, you will probably lose it all. Try multi tableing with two tables first. Once you are able to play two hands at the same time very effectively, then I say try three and see what happens.