Dancho Danchev had has some very good writeups on the current round of SQL injection attacks. This post on copycat attacks caught my eye, because it shows that there's more than one crew at work here.
If anything, this situation is likely to get worse. The tools needed to carry out a SQL injection attack are now almost available off-the-shelf, the attacks are obviously financially successful because they have been ongoing now for some months, and enumeration of vulnerable servers can be done through Google or Yahoo if you don't want to bother crawling the web.
Identifying and blocking domains helps, but it isn't a real solution. Most of these attacks are thwarted by a fully patch client (and I do mean all the software on the client, the Secunia Software Inspector can help here or some other decent audit tool). Using Firefox + NoScript is a good idea for the technically savvy. But ultimately, the best way of fighting this is to secure or shut down infected SQL servers. Don't be afraid to use the abuse@ email address where a web site is posing a continuing threat.