Somebody needs to sell something very desirable and only accept bitcoins as payment.  Maybe one of the Canadian MOM companies can be persuaded to accept bitcoin.

But more importantly than this is: Safety Safety Safety, people need to be assured that bitcoin is foolproof against attacks from powerful adversaries (this will obviously come much later).  A method of rating merchants who use bitcoin (i.e. reputations) might also increase the sense of security.

They also need some way of knowing how their exchange of bitcoins into other currencies will be protected from snoopers.

I could be wrong, but I also think that the easier it is to use bitcoin in conjunction with .onion e-comemrce sites, the more popular it will become.