Hardware aside, WebOS by itself is a great mobile platform.
You can't seriously deny - if you spent any time with WebOS - that multitasking with it is just a breeze, and the OS is so intuitive that it only takes a few minutes to learn the basics and be productive on it. For tweaking, no rooting needed, just a turn Developer mode on and you could start customizing your device. And Palm even provided a tool to get the device back to factory settings in case you messed up bad...simply brilliant.
Unfortunately, as it has been Palm's tradition for the last few years, WebOS was released lacking basic functionality available on prior Palm devices, and the hardware left much to be desired in terms of quality and durability. Coupled with lack of effective company marketing, the OS so far has not been embraced by many on the developing community.
Sadly, I don't see a bright future for WebOS on the smartphone market at all. However, I am very pleased that Google has hired the man behind WebOS UI development to work on future Android versions. If Android adopts the ease of use of webOS future releases, it will make this the dominant platform for mobile computing for years to come.