Currently, 42 contacts on my MSN account, using Pidgin.
At a guess I talk to no more than 20, maybe 5-10 regularly.
I need to clean up all my contact lists and information soon.
I don't use Xfire any more, but when I did I had, I don't know, 20 contacts or so, and talked to about 3. Hence why I don't use it any more.
Skype - 2 contacts, talk to 1 occasionally.