Gravatar implementation

Most themes inserts a users gravatar which is great. But the problem is that most people doesn’t know what the hell gravatar is.

Is there a gravatar implementation solution for wpmu? I would like a tab where they can select their gravatar, basically. I guess it would be a signup box or signin box if they don’t have an account and a simple upload option if they have an account.

How has everybody else solved this? A simple link to