Well... c'mon! This screen argument is analogous to the Super AMOLED vs Retina Display vs AMOLED display argument that keeps going around WRT cell phones. We're talking about 3.5" to 10" displays here. In isolation, are any of these screens going to "disappoint"? I doubt it. Not to beat a dead horse, by the lowly AMOLED 3.8" screen in my HTC 7 Surround may be vastly inferior to Super AMOLED or Retina (or iPS) but who cares? Unless I'm playing "mine is bigger than yours" with a Galaxy S owner, I'll struggle on in blissful ignorance. I don't know if this argument "scales" up through 7" and 10" devices, so I may be speaking out of my...
However, having said that, I don't think that the iPad faces any significant opposition right now. MS needs to get a tablet OS/tablet version of Win 7 out the door if they want to be in the game while Android 2.2 (Froyo) and 2.3 (released today?) are still not optimized to run on tablets. The Samsnung Galaxy Tab is superior to the iPad on paper - spec-wise (at least WRT RAM and ports/features) - but is hamstrung by the OS and is, in my opininon, significantly overpriced (if Samsung wants to take on Apple in this market segment, they should be more competitive on price). Meanwhile, the Archos 9 Windows tablet has a restrictive screen! And a not very sensitive one at that... It also runs Win 7 Starter (or whatever it's called - no idea how well that works) . Archos' Android tablets are let down by Android issues and match the iPad on hardware spec WRT CPU and RAM. They do beat the iPad in other features, though - HDMI out, USB ports, microSD slots. In my not-so-humble opinion, they should have doubled the RAM, particiularly if they want to be in a position to upgrade these devices to Gingerbread (Android 3.0, which WILL be tablet ready, apparently).
So, from the perspective of the end-user, the Apple product "just works"! Android tablet adopters are fighting buggy FW releases, mis-matches between the OS, developed for mobile phones, and the tablet that it's running on, and Windows 7 tablet users really don't have many choices - these things don't really exist in the wild. I don't think this situation will start to turn around until the Spring of 2011, which will have given Apple a full year's lead and no dobut iPad 2.0 will be out, heavily improved.