[roundsquare]

Here's one way. Its a bit more inconvenient, but I think its worth the inconvenience.

1) GMail has an export to csv feature. Export your contacts.

2) Facebook creates a "import contacts" feature. Import the list.

Done.

I can't think of any right now, but you may be able to come up with a feature that absolutely needs you to put in your email password. However, I suspect that by adding a little inconvenience, one can find a way around it.