I use a barely there case case with an Invisible Shield and it works like a charm. Still compact enough to fit into my holster with the added bonus of having the matte black look that I was hoping for in the 3GS
i have the case-mate barely there for my 3GS and i love it! very thin, feels good in my hand. no, it doesn't offer much protection for the chrome. but for me, my phone is either in my pocket, or it's sitting on the table/desk. not face down...
i can't speak for the clear cover because i don't use one. nor a screen protector. in fact, if i have to throw my iPhone in a briefcase or something, i use an old Oakley sunglasses bag to toss it in. perfect size!
ps-if you want some pics of a barely there case, let me know. i can snap off a few