If you're thinking of buying it, you can get pretty much the same protection from free progs like Adaware SE, Spybot, Spywareblaster and Spywareguard. I tried the free trial and it didn't find anything the free progs didn't.
I use SpySweeper the payed version and it can protects way more spywares that the trial version can. I think the trial version has around 3000 spyware fingerprints and the paied version have about 9000 spyware fingerprints. (I think it is called fingerprints.)
I don't know anything about spysweeper except what I said above so...
I find that it picks up a lot of scraps or inert leftovers. However, it's shields and realtime scan engine get in the way of just about everything! Kind of annoying. I find the MS antispyware program to do better with its realtime, and protection.
I can give you my opinion on version 4.03 of Webroot Spy Sweeper and it's excellent. Should you decide to buy it, go to Froogle.Com first and look for a discount. This is where I got my discount from