One table, I think, helps you learn about poker. Playing multiple tables, you are using what you know about poker, but I'm not sure how much you are growing as a player. I suppose looking back at hand histories is a learning tool, as can be the poker software available to analyze one's own play as well as that of their opponents.
Myself, I tried to go with the $/hr wisdom and got it up to 8-9 tables, but it was just too stressful -- if I got called away by kids or the doorbell or whatever, I was frantic. I've since scaled all the way back to one tournament at a time, and it's much more relaxing and enjoyable for me.
I'm taking notes, thinking about hands I'm not involved with, and playing in a style that more closely imitates what I would be doing at a live table, which is why I started playing online in the first place. Hopefully, when I do get to the WSOP
, this will all work in my favour