I imagine 10 is a good number to eventually shoot for, but it seems impossible to believe that the first 10 people whose blogs you like will eventually become friends of yours. You'll almost certainly have to make re-evalution of that list on a regular basis, and there are certainly those who - for whatever reason - you won't become friends with, but you will want to keep reading/commenting on their blogs. It's a very efficient way to develop friendships here though, I'll grant you that.