I multitable 4, but I worked up from 1 at a time v e r y s l o w l y, even so, if I time out of any table, then it"s down to 3 for the rest of the session. I also use the auto-fold button straight away if I"m not intending to play a hand, and move up cash game limits one table at a time rather than all 4 at once. Sometimes it gets a bit busy on all 4 tables, but normally things are ok, and I still manage to take notes.
Also, I keep detailed records of every session, so I can see where my tipping point is for profitability, as there"s an optimum number of tables for everybody. As you play more tables, your winrate goes down, but it"s compensated for by the increased number of hands up to a certain point.
One day I"d love to be doing 6 or 8 at a time, but 4 is fine for now! And it"s all I can fit on my monitor..!