As per Ebay rules, you have to wait at least THREE 
days before doing anything rash, otherwise it is 
your fault.  (Unless you specifically stated that 
you need to hear from the buyer within 24 hours.)

This happens all the time.  About 1/3 of the 
sniper bidders that win my auctions don't contact 
me until the very last minute, even if I e-mailed 
them as soon as they won the auction.  There are 
many possible reasons.  Maybe they aren't using 
the same computer they use for their mail.  Maybe 
they aren't ready to pay immediately so they want 
to stall for a day or two.  Who knows?

Yeah, it would make sense that they are online, 
but you can't assume that.  (I've been lucky.  My 
last two auctions were paid for within about 3 
minutes of being won.  Paypal can be so cool 
sometimes!)

JP