I've been playing around with it for a bit now. The UI definitely has upsides and downsides. A hybrid between WebOS and Android could be awesome. Some things are better on WebOS, some are better on Android. There is a really great RSS/Google Reader program that I'm digging called NomNom or something like that. I also got the Preware repositories set up. I got a kernel that allows me to run the CPU at 1.5Ghz and, among many other things, a funny mod that changes the "Just type..." bar (universal search) to be the "Make it so..." bar.
WebOS's web browser is great as well, but I can't figure out how to remove a single bookmark without clearing the whole list. There's probably a way to do it, but I haven't bothered to look around too much. I've also got to say that WebOS seems more stable than Android (I've used both 2.2 and 2.3 on my Droid X). It's also easier to "hack" WebOS through Preware than it is to hack/root Android on my Droid X (where I lost root during the Gingerbread update and don't want to SBF to get it back again). HP actually seems to be completely fine with people hacking the shit out of WebOS, which is cool.
Now the bad things...
Compared to the Android, there just aren't a whole lot of apps. There's no camera app that I know of by default, and there's no rear camera anyway, so I haven't bothered to download one. It still seems silly. The Touchpad also can't compete with Google Maps navigation (luckily I don't need or want it for that). The Touchpad could also be called the Fingerprintpad. At least I have it in a case now which is nice. They also decided to use a proprietary voltage level through the USB charger which is higher than 5v that you get from a generic wall socket USB adapter. I have USB plugs attached to a couple sockets in my condo but can't use them...at least without getting yelled at.
Is it worth $500? Hell no. Is it worth $99? Hell yes. It even came with a free 50GB cloud storage account for life (not tied to the Touchpad). Maybe at some point I'll get Android on here, but for now WebOS is perfectly fine. I have the Kindle app and I'm happy.