mayankleoboy1 : WebOS has such a good UI that RIM's playbook seriously rips it off. It is roundly considered a great OS on underwhelming hardware.
It has an excellent multi-tasking metaphor and the primary UI is gesture-based. No app manager is necessary.
Swipe up from the control area (a touch-sensitive area below the screen) to show running apps in "cards". Swipe left/right to bring other apps to the front. Swipe up again to bring up the app-launcher. Touch an app-card and you can move it left-right to organize the open apps. "Throw" it off the top of the screen to close apps.
Swipe up without lifting your finger brings up a "wave bar" containing 4 of your favorite apps. Move your finger over the app you want, lift up, and it launches.
It has an excellent notification system. The notification area (located at the bottom of the screen) switches between an icon mode and an information mode. Both can be used by apps to enable controls (usually for media programs). Icon mode will show the icons of any notificaton-bar enabled apps that are running, and icons indicating new email, text, phone notifications.
Tap the icons to bring up the information mode. It provides information on several different events simultaneously (i.e. latest text message plus number of other unviewed texts, last missed call plus # of other missed calls, latest email title plus # of other unviewed emails, etc).
The notification area is active even when the screen is locked, which allows you to see if anything worth unlocking the phone has happened. It also lets those notification-area enabled apps be controlled even through the lock. This is really handy for audio apps (my favorite, Dr. Podder) so you can play/pause/forward/rewind without needing the smart headphones or unlocking your device.
WebOS 2x (currently only available on Pre2, supposed to be released for all devices soon) adds the ability to group apps into "stacks". It also includes additional notification modes for when the phone is on the charger that will enable some form of widgets.
Unlike most devices, the menus are very useful and most things are accessible quickly (3 touches to change which BT device I'm using, turn wifi on/off, etc).
It also has something called Universal Search (1.x) that has been upgraded to Just Type (webOS 2.x). In WebOS1.x in the launcher screen or any of the minimized-app views you can start typing and it will begin autosearching the device. If I type the letter "a" I get my wife Angie's contact, a list of apps (Agenda, Amazon Deals, Angry Birds, App Catalog, etc) and the "Find" option, which let me submit that entry to Google, Google Maps, Wikipedia search, or Twitter Search.
Just Type will add additional options, like letting you send the entry as a text, create a note, calendar appointment, or send that data to any other app that registers a Just Type entry.
One of the biggies of WebOS is that it's not locked down and can be put into root/developer mode simply by typing "upupdowndownleftrightbastart" into the universal search. A window asks if you're sure and bam, you've got root on the device. You can now sideload whatever app you want. The most popular side-loaded app is PreWare, that not only has a repository of apps but GUI/OS patches that modify the operation of many things.
WebOS really is a web OS. The GUI is html/javascript tied to a sql-lite DB. You may recognize this as the basis for HTML5. So you can customize the OS appearance and operation to an amazing degree. I've got about 4 dozen patches installed that do everything from changing the number of apps visible in the launcher to having the camera app accept volume-button presses to take pictures.
I've got a Pre- (the original Sprint Pre) and overclocked to 720Mhz it's a spiffy experience. At the default 600Mhz and only 256MB of RAM it's laggy. The Verizon Pre+ with 512MB ram is better but still not buttery smooth as it is overclocked.
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