I had the BSE skin on my 1st gen iPhone from July 07 to July 08. Over the last month the edges were turning loose pretty badly. I keep my iPhone in my front pocket, so dirt and lint tend to collect at the edges of the film. I really like the extra tack the film gives the iPhone, so it's way less likely to be dropped than with it naked. It also maintains the aspect of the iPhone making it easy to slide in and out of my pocket.
FWIW...
I have not seen nor tried the IS, but I recently replaced the BSE with
BodyGuardz. It offers a
much better fit and the corner flaps are much smaller, so it appears less likely that they will peel back with use.
I also applied
BodyGuardz for 3G iPhone to my new iPhone 3G. It was a lot tougher to apply, but I think the 3G is more difficult because the design uses more compound curves.
Also, BG and IS offer lifetime replacement. The BG came with 2 sets so you can replace the used up film, request a new set, and then send the old set back. There is a $4.95 handling charge though.