The skins are of varying usefulness. Those not inclined to tinker probably like them more. You can get most of the usefulness from other apps if you so choose. I believe it is Acer who allows you to choose to use their skin on bootup which I think is genius and should be a requirement for all manufacturers.
As for the carrier stuff, I guess the one benefit is that it could help lower the cost of the phone. I’m still crossing my fingers that T-Mobile gets a pretty standard SGS II, but $800 to get it off contract is a pretty high price. I can deal with some bloat to bring that down to $500 or so.
Yeah, it’s just what Launcher you decide to use. The manufacturers all have their own stuff. HTC has Sense, Motorola has Motoblur, Samsung has Touchwiz, Sony has the Arc.
Amazon has the SGS II for $699 off contract. I’m expecting it to be the typical $200 once it starts hitting US carriers. The MSRP on my handset was ridiculously high when it was released too, but obviously I didn’t pay that.