The avatar creation tools are pretty straightforward and won't really stress anyone who's used Second Life's appearance editor. If you're not cloning your head from an image, like I did, you'll find a large variety of presets for each part of the body. And that's actually where Evolver shines.
Evolver allows you to take any two body-part presets (two faces, two sets of eyes, two body-types) and allow you to blend them together, using a simple slider. This vastly increases the possibilities available, far beyond what any reasonably finite set of components would normally allow.
Registration -- and indeed the whole service -- is free for the moment, and supports (or is in the process of supporting) Second Life fork RealXtend, Wonderland, Torque, FaceFx, Activeworlds, 3DXplorer, Cobalt, ExitReality, Unity3D, VastPark and Worldviz.
Right now, the tools don't seem to incorporate any other position other than the stock-standard T-pose, and clothing options won't knock your socks off (no glasses or accessories!), but the models apparently come animation-ready for their target-environment.
I took Evolver for a spin with a headshot from Second Life, and it all worked out fairly well. I started out with the shot you see on the left, and wound up with a detailed mesh (the one above) in only a few minutes. Having been through the process once, a second attempt would probably yield even better results -- I could have tuned the face-shape considerably, but left it as-was. Evolver is still in alpha, and has a ways to go, but it looks very promising already.
Truly portable avatars? It certainly has a lot of potential.