I usually play between 2-4 tables at $1/$2 NL. It really depends what your purpose of playing is though mate.
If your goal is to play top notch poker then one table is probably a good idea as you can focus on making quality reads and getting maximum value from every hand.
However if your goal is just to make money then you are probably better off playing a very NITTY game and mulit tabling. You will find that your bb/100 hands will drop but the amount of hands that you do in an hour will sky rocket making your hourly rate more profitable.
I have a fairly interesting situation where I can spend my whole day doing poker activities and call it work.
Basically what this means for me is that I can play boring unimaginative nitty
poker online and garner a nice profit and I also get to the casino for some live poker at least 4 days a week.
Obviously live poker is the slowest thing ever and I use that fact to my advantage. Where I play about 200 hands per hour online we would be lucky to play 30 at the casino. That means I can focus alot more on ' playing poker' then on just 'having an edge'.
To summarise this obscenely long and pointless post I will say.
It all depends on what you hope to achieve.
If your goal is money then multi table and tighten up.
If you want to become a better poker player then play less tables and focus.
Hope this helps!