I'm not aware of anything that can rank contacts by some function :/ I'm pretty sure GMail doesn't give you that data, unfortunately...

How does Xobni get it? I'm sure you could hook into the API and get at least an approximation.

Ah, I wasn't sure they did this, I've never used Xobni. I think they just get them from your emails (it looks like they have access to them), but I'll look into it more as it could solve this problem, thank you.

Can you do counts on the 'Sent Mail' folder?

I don't have any sort of access to the user's mail, I can use a small widget that imports contacts from your email provider but for anything more involved I'd basically have to write my own importer, which is a lot of work.

I was foolishly thinking you had IMAP access to the accounts. Nevermind.