I'm owning two right now, though it's too early for a final sentiment. Saving configurations on the controller seems to be a feature that is currently in the Steam Client and Controller Firmware Beta, at least from what I've understood.
Baseline right now is: The touchpads are NOT suited as an analog stick replacement for the steering in racing games, but are a little bit better than a D-Pad for 2D platformers if you configure them correctly. If you want to control a camera, they do a decent job, as a trackball on the desktop it works quite well if you need it. The triggers can also easily replace regular shoulder buttons, the tactile feedback on them and the touchpad works great for digital input. You can really feel when you cross the activation border, it's a completely new feeling.
Initially I thought you could only pair a single controller to each wireless dongle, but you can actually connect four per dongle, you just have to pair them manually once in the client.