SFS e.g. gives you the frequency value back which tells you how often ip, username and email are reported to SFS. In your application you can use this value to reduce false positives. Also e.g. you can say only block posts or user registrations if ip and email are listed. I have prepared my implematation to use the frequency. But at the moment I've set the value to one. I haven't gotten any false positive with SFS by now. But I don't block only for username.
SFS is a good database. But SFS doesn't offer the applications which can been used to use SFS. BTW: It's the same thing like it is with IP-RBL DNS blacklists. ... And BTW II: Other anti-spam features are producing false positives, too. ...
Please excuse my bad English!
@callum: Why you haven't gave me any feedback? When did you test ABM? Which version of ABM have you tested? Please answer per PM not to be too much off-topic here.
BTW: Double request for Akismet: viewtopic.php?f=105&t=35022