Come iPad release - there will start to be comparisons made to what is in the market for alternatives.
Until Windows comes out with a new version, it's apples and oranges for having Win 7 on a tablet. Android will likely show up earlier and be a better comparison.
Is there a decent pony for non-iPad likers to back? It's a problem for haters. They can want their USB, cam, moon on a stick right now, but they don't have many in the market alternatives.
And then the other issue is - when there are alternatives, it'll be like the problem iPhone killers have - there will be another iPad killer, that instead of killing the iPad, just succeeds, and makes obsolete, the previous alternative.
E.g. see the Droid, Nexus One, Legend, Desire.
Once the rivals get the hardware, they're still stuffed until they sort their software. And then by then, I'd imagine there will be a rather nice line up of iPad specific apps and the book, video, music purchasing systems will be kicking in. And that's a hell of a positive for the iPad.