I'm a longtime MalwareBytes use, and I've recommended it to dozens of people. The only reason why I'm here is because SUPERAntiSpyware is better.
Long story short, last week I got infected badly with spyware. The trojans/viruses deleted MalwareBytes, and kept deleting it on install. When I finally got it installed it removed several items, but it fail to detect 3 trojans. That was major because some of them were loaders. The only thing that saved me was a trial version of PC Doctor being stalled, so it kept blocking the connection attempt. Even after I updated MAB's definitions and did several complete scans it still failed to detect the remaining 3 threats. I figured it might be a false positive so I just disabled PC Doctor. I was re-infected immediately after reboot, MAB was deleted again, and I was back to square one. I just gave up and formatted. After reading this article I decided to switch and I've never looked back. Earlier this week I was almost infected again, and SAS removed everything (although it seems to be unable to detect this registry string).
I love MAB and I've used it forever. But there are new high level threats that MAB can't handle.