Neo>Slider
I've had my Capsule for about a week now (ordered from ebay and got a free car charger with the new case for around $29 shipped...strongly reccomend doing this) but I love the case, best I've had so far (had Griffin Elan, Casemate Slider, Speck Candyshell)
Without a doubt the Slider DOES scratch the back of your phone, pretty much only where the two vertical pads are. Another bad thing is that the finish wears off after a while, I had the black matte finish and it wore away within a month or two, leaving the shiny black finish showing. It is a tight fit but IMHO the Neo is a better one and is much slimmer. It wasn't that difficult to put on, took me about 5 minutes to get it right. I didn't care for the screen protectors it came with so I put an anti glare on from the apple store (can be put on without taking the case off). Another nice thing about this case is the variety of protectors you can use with it - unlike the slider which will only accomodate the narrower ones. My only gripe is that the rubber "condom" you put on first does attract some pocket dust/lint where it covers the lock button. Apart from that it is very good looking, offers great protection (gotta love the two inserts to protect the headphone and connection port)
Sidenote: the Speck Candyshell is also a good case but costs more $$, scratches easily, and the small section around the docking port breaks due to the fact it doesnt leave enough room for larger plugs, which stretch/crack it over time