Most writers on the subject of online poker do NOT advocate multi-tabling. Most notably, John Vorhaus - who believes people multi-table because they are action junkies and get bored by playing just the one table.
Furthermore, it's true, multi-tabling goes against the whole idea of being able to study your opponents and playing your "A" game.
In saying all that though, whizz over to the 2 + 2 forums and you will see that most of the players making serious money DO actually multi-table. Some in the region of double-figures!!
Now for us mortals, it's hard to figure out how this can be profitable but the only way I can understand this is that these guys must just eat, sleep and dream POKER! They MUST have been playing for so many years, endlessly, that all their moves are virtually automatic and they KNOW EXACTLY what they are doing.
Now I only play poker at the low limits and my suggestion might not carry much weight but I have tried multi-tabling (Limit Poker at Party Poker
on 3 tables max - any more and I am out of my depth) and, indeed, it just felt like I was playing like a machine. In other words, far from making poker more interesting, it actually made it quite dull. Additionally, you miss all the subtleties and fancy moves that makes poker so compelling in the first place.
If you are happy to play poker instinctively, like a robot, in a monotonous fashion then fine - I would recommend playing the low limits first and moving up VERY gradually. You don't wanna just dive in to multi-tabling 4-6 tables straight away.
Nevertheless, in the spirit of No Limit Poker where it's all about psychological warfare and ducking and diving and wheeling and dealing, surely single table battles are where it's at.
Nah, leave multi-tabling to the big money making mechanical experts.