Not because it's got spyware in it, but because of the complete and utter usability FAIL that resulted in my temp folder being emptied.
Apparently the latest version on startup counts the number of files in your temp folder, and then offers to delete them to increase scan speed. Sounds reasonable? Well, this dialog also has a 14-second countdown, at which point it will then go ahead and delete them anyway. Also sounds reasonable? Well, because I've got both my web cache (with quite a generous quota) and an awful lot of other files in there (~50,000 total), it took Spybot some time to count them all.
Which meant when it popped up its dialog I didn't see it, because I was doing other stuff. And yes, all 50 thousand files got deleted without going via the Recycle Bin. And yes, maybe I shouldn't have been using a temp folder for files that I might have wanted to hold on to. That still doesn't excuse Spybot's behaviour.
It's my computer damnit.
Update: There is, apparently, a registry setting that may or may not disable this behaviour (there's some reports that it has no effect on Vista). Yes, the only way to control this behaviour is via a semi-documented registry setting that the average user will not know how to change.