IANAL, but my understanding is that trademark law is based on the idea of avoiding confusion in the marketplace. It's possible to have similarly named products in completely different industries without violating trademark law because they won't confuse potential buyers of the product.
THAT said, I'm not sure I personally would take the gamble!
Oh yeah, that's a good point. Given my understanding of trademarks, I'm not sure Terminix's claim would hold up in court, _but_ that's irrelevant because people don't generally want to go to court. I doubt 37signals would go to court to keep the MRSK name.
THAT said, I'm not sure I personally would take the gamble!