I have the Streak 7 and I have to say that I love it. The form factor is just right and, despite the screen resolution and lack of Honeycomb (something I hope they will rectify at some point), it's a great little tablet. I have a lot of confidence in Dell's ability to create a great 10" tablet, as well, as long as they take the criticisms of the 7 seriously. If they get their heads in the Android game they will be contenders and have the potential to blow most of the competition away in the price department.
That said, they will have to work hard to keep the weight of a 10" tablet down, as the 7 is almost too heavy. For my money, though, a 7" tablet is just right; anything bigger is too unwieldy for the way I use it.