Do note the "no commercial use" clause on the free certificates. Not an issue for any of my uses but it may affect quite a few people. Though I'm not sure how they would enforce this.
Of course if you can't afford $60 for two years for the next grade up, then your commercial venture is probably not a roaring success!
Revoke the certificate.
(other than regular whois lookups assuming that data is correct (probably too much hassle), checking the sites secured by the certificates (even more hassle), or someone "dobbing you in")
I'd imagine the file gets large after a while, but we've had ways to ease distribution of large files for quite some time..
Nevermind the fact that CRLs are of dubious value, anyways. See: http://people.csail.mit.edu/rivest/pubs/Riv98b.pdf
You do pay a $60 fee for identity validation, which is valid for 2 years. You can also have automated validation, but they don't allow wildcard certificates (which I sort-of understand, they do need to make money some way right)
So you get unlimited free non-wildcard certificates or unlimited wildcard certificates for $30/year. Not a bad deal.