Please do. I went through three cases before I found one that wasn't even more slippery than the phone itself. Turns out the Terrapin case is very grippy but it's really hard to press the buttons on the side. Maybe it would have gotten better over time, who knows. I've only used the case for about a week or two, then decided the hassle isn't worth it and went back to the orange shell with no cover at all.
I've since replaced the 635 with an 830 that I'm not too happy with. Might return to the 635 some day if Microsoft doesn't fix the apparent issues with the 830 (auto reboot, lost wifi).