I’ve been spending more time with Facebook lately and I’m very impressed. Not only does Facebook make it incredibly easy to see which of your email correspondents are on the site, they also prompt you to upload your AIM contacts.

FB AIM Upload

Viral prompts are integrated into every aspect of this site’s behavior and it works. For example, I tagged a friend in a photo and as I typed in his name, a subtle email box appeared asking if I wanted to let him know.

Facebook Photo Tagging

What’s great about this is that it’s contextual, not intrusive and feels useful as opposed to spammy. No wonder they’ve been growing like crazy.