For a lot of services, verifying e-mail addresses is primarily a means to filter a majority of spam accounts - think bulletin boards, buy/sell sites, etc. It is by no means perfect, but it's an easy, low-hanging fruit. It is only secondarily a check to see if the user misspelled his or her e-mail address (which is often checked by having two e-mail fields and comparing them). I would still say that tracking down a mi…
Perhaps a notification after a few days along the lines of "verify your email address is correct" top of the page in cases where it appears they haven't received your welcome email would be more appropriate. Rather than barricading them from using the service.