I've only had to deal with Customer Service / Repair once, and that was with Microtech (Scarab wasn't locking closed or firing open). It took about a month, but I got my knife back fine. Of course, right after I sent it, 3 hurricanes decided to hit Florida (one of which came back for a second dose of fun), so that might explain any inordinately long turnaround. I keep hearing about MT's bad customer service, but I had no problems. I'll guess I'll consider myself lucky.
I don't like their proprietary screws though, and that in itself says something about CS. With, Kershaw, Buck, and Benchmade, I keep reading about replacement clips, screws, torsion bars, etc being sent free. Yet not only can you not adjust a loose MT screw, you're required to send the knife in. Which is a major PITA for an auto, especially if you're in one of the states that doesn't allow autos, which is most of them. Their newly announced CS policy is even worse.