Are there any websites describing it, or do you just have to grab the SDK? Android is really bugging me with its quirks, like animating a view's graphics while leaving the views interactive element behind. The idea of PSS is good, but we really need to see that there's going to be a userbase. Add PSS support for PS3 and I'm probably in.
So far as I can see the SDK tells you the most the quickest. Above all, everything is fast. This is probably one of the fastest things I've ever got installed and up and running for development so far. It's vastly less complicated than Android, more close to Windows Phone 7, but with the current Dev environment being much more lightweight than a Visual Studio, it's very quick to load the devenv, a project, and then build and run a sample project and start up the emulator.
There are certainly still some bugs (from what I'm reading in the forums) and some missing features, but overall it seems quite good actually, from the short time I've spent with it. You can get the apps/games onto your Vita pretty quick as well and they stay there.
In terms of userbase I think there's potential here for Android crossover, as this really seems a LOT easier than Android development (although there are still some limits - sometimes relatively basic stuff is still missing, like access to GPS data or getting the device orientation are on the to-do list, though mind you I can imagine the GPS thing, that's a tricky one to get right in terms of use, privacy etc).
I'd say download the SDK and give it a spin. You'll have it up and running and tried out most of the examples in less than an hour, and it comes with the docs as well.
EDIT: gaf thread discusses it with at least some screenshots of some of the better looking stuff. It looks like especially the GameEngine2D that was added relatively lately, is proving useful. Though the 3D stuff looks ok as well, and again relatively easy to do.