I've used both and also thought of moving to WebOS when Nokia committed Microsoft suicide. However, now that HP has thrown in the towel, there goes WebOS's advantage of being a supported OS.

WebOS isn't nearly as fun as Maemo5. Just getting a terminal that came CLOSE to working as well as the built in X-term in the N900 was a real struggle. Not to mention the portrait keyboard is missing many keys that are needed for command line access, and no symbol key menu is available in the majority of terminal apps on WebOS.

WebOS also has no X server by default, and the X server you can install on the side is buggy and only accessible via VNC. With that fact, you can forget about simple ports of applications from desktop linux or binary compatibility with apps compiled for Pandora.

Also, the packaging system, while managable, is not nearly as efficient as the Debian method used on Maemo.

The speed and UI is really nice on WebOS, but without the promise of new hardware and varied form factors incoming, it's hard to justify the investment of your time instead of just upgrading to a more familiar and flexible N900.