Like Hugh - I've also been hit by the nightmare spambot that is Quechup.
Frankly - I'm feeling pretty stupid as I should really know better BUT this looked credible. It's pretty shifty to spam everyone when all you're doing is checking your address book for others you know in the system, though, but he ho lesson learned the hard way.
I'm really hoping people will vote with their feet on this one and the company responsible for inflicting Quechup on the world i-date are forced into bankruptcy quickly.
If you've received an email from me asking you to join Quechup please delete it immediately. I have not and did not agree to this being sent out. I am REALLY, REALLY, sorry if anyone has been caught out by this.