webOS user for about 4 weeks
I bought a 49UB850V a few weeks ago, and so far have been very happy with the Smart functions.
Everything is controlled from the same GUI, so not just the 'Smart' functions, but also things like picture and sound settings etc.
The Magic remote works well, just like using a Wii remote, the standard IR remote hardly gets any usage.
I also plugged in a wireless USB dongle (HID compliant), for a keyboard and Mouse, and it just worked. With the mouse controlling the pointer, and keyboard allowing text entry etc. Useful for search inputs, or when adding YouTube account details etc.
It also plays MKV files (including over DLNA if your server supports it) , which was a nice bonus for my, ehem, library.
There are quite a few apps that can be downloaded form the built in store, although so far I've not tried any of them.
Annoyingly the official Android app is just a place holder currently, due later this year apparently. But you don't need it to do things like send Youtube feeds from your tablet/phone to the TV, as the standard Youtube app recognises the TV anyway.
There is still room for improvement though. the DLNA client doesn't show folders, it's just one large list of everything. With the only filters being by type (video, pictures, music).
But it's early days, and the system has already had one update since getting the set, so I expect more will be coming.