I love Domeskin. They're like standard film skins but are thicker, giving them an almost 3D look and feel. I have been using them for a week and, at first, I put them on because of the beautiful look and matching wallpaper. Almost immediately after that, I came to appreciate Domeskin for the wonderful feel and extra grip they provide for my iPhone. With Domeskin, when I place my iphone on a surface, it will stay in place and I don't have to worry as much about it sliding to its doom, or being nudged into oblivion. It just stays.
Also, the two Domeskin appliqués on the front of the iPhone make sure that your glass will be protected from scratches. That makes Domeskin not only much more fun than a regular skin, but more protective as well.
The downside to Domeskin is that they are not able to be used in conjunction with most cases. If you have a loose fitting or stretchable case then you may be able to fit it over the Domeskin, but it still might be tight, and you'd still likely have trouble removing it. Think of a Domeskin in lieu of a case. (You can, however, remove a Domeskin and then reuse it later.)
Domeskin are great for anyone who wants to liven up their iPhone, and get better grip, with more substance that a standard skin but nowhere near the bulk of most cases.