CR rated them on blocking, features, and ease of use. The features rated are "Protects browser", "Protects start-up", and "Describes spy-ware".
Spybot scored "very good" on Blocking, "very good" on features", and "very good" on "ease of use." It's a Consumer Reports Quick Pick Recommendation.

F-Secure (#1) and Spy Sweeper (#2) scored "Excellent" on Blocking, "Excellent" on Features, and "Very good" on ease of use.
Spyware Doctor (#3) scored "Excellent" on Blocking, "Very good" on Features, and "Very good" on ease of use.
Trend Micro's product (#4) scored, respectively, Excellent, Excellent, and Good.
Ad-Aware (#5) scored Very good, Excellent, and Good.


Soooo... Spybot apparently doesn't pick up as much "dirt" as some of the other products; because it is free, though, it is recommended. What I like about CR is that they make it extremely easy to pick out either the absolute best performer (in this case, F-Secure) OR the best VALUE (in this case, Spybot). The vacuum test you're referring to, I assume, recommended a 50%-picker-upper over an 80%-picker-upper because the latter cost 10 times as much...