I personally would never ban a whole TLD
hotmail.com, yahoo.com, etc are all used by spammers as well
The ability to ban TLDs would reduce the amount of spam my forum gets by at least 90%. Banning .ru and .info alone would halve the spam problem on my own board. It would also mean I wouldn't have to spend 2 hours per week deleting/banning spam sign-ups.
My community was small (around 30 active members) but it has effectively died now because of the spam, it's a shame.