There is no denying that iOS is the 500 pould gorilla of tablets, apple is enjoying much the same success with the iphone and ipad as Microsoft did with windows. So apples not in any danger whatsoever from the current crop of tablets.
That said, IMO WebOS is the by far my favorite of the competition, and from a developers perspective is an infinitely more comfortable environment than iOS. I develop and have a touchpad, ipad, ipad2 and honeycomb tablet so improbably a bit over exposed lol. My iPad2 is my daily driver but with a few small changes that could easily change to the Touchpad.
The touchpads problems...
Casing / Size
While i like the iPad like size and screen aspect ratio better than honeycomb wide screen devices the touchpad is too thick and a major fingerprint magnet. HP has a fondness for piano black gloss plastics that they really need to get over IMO.
OS
The OS is actually really good, does multi-tasking app switching so much smoother than iOS and its 'fun' to play with. But it lags, and a tablet should almost never lag. As it turns out all of its lagging issues are easily addressed with patches from its homebrew community to disable logging and make a few other adjustment. Once thats done its a MUCH IMPROVED experience, HP just needs to make their product work that way out of the box.
Apps
No one can currently compete with iOS app advantage and until a device gets a foothold developers wont develop for it so its a double edged sword that makes it tougher and tougher for a new platform to take root. WebOS does have more TABLET apps than Android though and the numbers growing.
Price
The Touchpad came out at a $499 (16gb) / $599 (32gb) price point just like the iPad. Obviously its not an equal value, but HP routinely prices high and discounts with all their products. Prices are already down to $399 / $499 and there are $50 discounts off that right now. At $349 the touchpad isn't that bad a deal.
Strengths down the road.
HP has announced they are putting WebOS as an instant on option on their PCs and printers so in time there will be alot of WebOS devices out there by default at which point they might pick up a critical mass of developer support.
I picked up my touchpad at Costco so have a while before making my final decision on it, but right now about 90% of my tablet development work is on the touchpad then i Port/Test for iOS and Android. The touchpad dev setup is just more my style.