I recon that these scams must work well enough or they'd not bother.They most likely send out several thousand at a time and the majority do not bite but when it all just spamming out anyway it is not like it takes much effort.
I also have a feeling that many of these e-mails are coming from "zombie computers" that have already been infected and it just propagates even if the majority do not fall some will.
http://en.wikipedia.org/wiki/File:Circle_of_spam.svg
What Skybird said is true a system Restore will not do anything to a virus in most cases unless it is a real amateur job.Usually they simply hide themselves in the system restore temporary files which means they'll come right back and the better ones will lay dormant for a few hours or days.
P.S. I love No Script.