I think one of the bigger turn offs might be the fact that the new owner will have to get everyone to setup their payment method once they switch. Because the current payment system relies on 37Signal's own.
My guess is they just put the listing on flippa to attract attention. I'll bet there have been bids but nobody is paying attention to the listing and accepting them.
They certainly haven't done any of the basics, such as answering questions. One commenter wrote, "For all we know, he is dead as he has not replied to ANY questions."
I, for one, am not impressed by their behavior. It just screams arrogance.
I wonder why they are not accepting any Bids, one has been pending for over a day now.
That means they got at least one bid.