I tried the Belkin Holster (bought and returned) and the Griffin Elan Holster (at an Apple Store) and then bought the Griffin Elan Snap-in. The Belkin and Griffin holsters were too tight that it was a real push trying to get it in. And even the salesperson at the Apple Store who opened the Griffin Elan for me to try agreed that he too would be scared of throwing the iPhone across the room by putting too much pressure on it to pull it out. iLounge reviewd these cases with a C+ rating. There was a 3rd holster that they liked slightly better and that was the Marware has the C.E.O. Sleeve for iPhone, but I imagine it may have had the same problem. I couldn't find one. I read above that someone said the Belkin stretched over a few days and now was too loose. To me it should be loose enough to pull in and out of quite easily but not pop out if you jumped up and down. Don't turn it upside down.
Anyway, in the end I got the Griffin Elan Snap-in and am very pleased. It fits securely but comes out without too much force. And you can turn the screen in or out for protection. Plus it has holes in the bottom to hear the ringer and a opening so you can plug in a charging/syncing cable which is great for the car.
My ideal case is not a holster though I wanted one too, but a soft pouch. I ordered over the weekend and will have in a week or two (coming from Australia) a foofpod bag. They look great and have been highly recommended. Check out
www.foofshop.com . I had a Nokia 8801 for the last 2 years and that came with a small suede pouch to carry it in my pocket. The whole phone was stainless steel and it still looks brand new, not a scratch anywhere on it in two years. When I get my foofpod bag I will most likely carry my iPhone in that in my pocket most of the time, but still keep the Snap-in holster for occassional use.
BTW, I also use the Powersupport Crystal Film which is awesome. Having had their film and case for my Nano, I bought the film before my iPhone just because I knew the Apple Store would sell out. I highly recommend this film to everyone. Goes on easy and comes off if need be. And the responsiveness and clarity is like it's not their. Smudges just like the screen would, but I use my cloth to clean it up.