>Apple will wipe the floor with them all. Not because it's better but purely because they got there first
Having played with an iPad for the first time today, its no great surprise MS and HP are backing off the form factor. It wouldn't surprise me that much if Apple get there alone. Certainly if iPad is the gold standard, the pretenders will be utterly poor.
Manipulating it to do anything useful is difficult, you can't lean it at angle or use it one-handed other than for simple input, click and scrolls etc. Laying flat and leaning over is the only way to edit and that process with text documents is very slow and awkward. With keyboard onscreen you lose too much of the document to do any serious work.
Even with a keyboard (which seems to defeat the point) its awkward without an ad hoc stand to angle the screen, then you're constantly readjusting since keyboard navigation alone is not possible - and then you're also plagued by the grease that accumulates and a less than perfect viewing angle. Most people seemed to default to keyboard on lap, iPad on table and a kind of Gatesian rocking motion or orangutan arm posture. As a laptop replacement folding stands will be order of the day, as will carrying keyboards - ideally one with a trackpad or pointing device - but ultimately the screen is too small and the current software inadequate for actual work.
Its basically a view only device - and then one with a rather limited and annoying experience online, aside from the number of sites which don't display properly and the dodgy wifi, anything requiring input has almost the same slow, iterating-irritating experience of browsing using your phone.
The idea that this form-factor is better or even equivalent to a netbook or laptop is very far from the truth and if its filling an untapped niche it wasn't one I or the died in the wool Mac fans I was with could see. From a UX or ergonomics perspective its actually a pretty bad idea.