Jed Hartman posts a warning that if you let Quechup search your email records for other users it will spam your contact list to get other people to sign up.
So don't do it.
In fact, be wary of any "social networking" site that asks you to do this. As he recommends, check the net and see what other people have to say about a site before signing up.
I personally received three copies of my friend's invite to join Quechup, so I was suspicious already.
ETA: and when I tried to cancel my membership it says "Unable to log deregistration details." -WTF? lame lame lame lame lame.
(second attempt to cancel, using one of the set causes instead of 'other' appears to have gone through.)