This program has gotten very good reviews by most of the anti-spyware community experts. It's one of the few programs that can find rootkits (malware that hide themselves from normal detection).
BUT, the program uses a HUGE amount of CPU resources to do this. If you have it startup at boottime, especially if you have an anti-virus program also doing a boottime scan (which you better), it slows your system to a crawl. I have it on 3 computers - on average it uses about 50% CPU to startup!!! So I recommend NOT doing a boottime startup. There seems to be another problem to me with doing a boottime startup as well. Until the program is fully loaded, the system tray icon doesn't appear, so you can't exit from this process if you need to, except by going into Windows Task Manager.
On a manual startup, the program takes a couple of minutes to load the database and monitors - and that's on a very healthy Pentium 4 3.0Ghz! There is also another problem - with the automatic updates. After the program updates it wants to restart the program. This is not working correctly - it leaves the first iteration and starts a second iteration, which takes EVEN longer to start. Then you have to manually shut down both iterations and REstart the program manually it seems.
So, problem free? Nope. But I still recommend this program. If you can live with the bugs, it's VERY good at what it does.
(Always be sure to use more than one anti-spyware program. There is currently NO one program that catches them all!)