I use IS and have had no issues with it peeling or anything that like. I've used IS on both my 3G and 3GS, as well as my non-related phones... like my DS and my DSLR's screen.
I had a simple back from BS. And put an Incase slider over that...didn't think it was going to come off! I like the simple back because it's a lot easier to put on. It protects the phone when it's laying on it's back. Now I have a white phone so all if them will turn yellow/brown as time goes on. So I put the Skullcandy hard white case over my simple back BSE and it's great. Don't care if the case gets scuffed. My wife has the black phone so she just has the incase slider without the BSE since it felt like it would never come off. It finally did but it wasn't pretty. The incase doesn't seem to leave any marks on herphone casing.
Posted from my CrackBerry at wapforums.crackberry.com
Hands down the invisibleShield is the best for the body cover only. The screen protector is not that good, it doesn't get crashed but has the orange peel. For the body it covers everything that needs to be covered. For the orange peel you will notice it alittle, but it doesn't peel up on the edges like the others. It is hard to install but is well worth the money. I only wish it came in body only, you have to buy screen and body for $25 or so.