I've got a Motorola Droid, which definitely biases me. Here are a few thoughts:
(1) There is a flood of iPad clones coming. Several low-budget Chinese rebranded tablets already out there, and several "mainstream" ones coming by the end of the year (HP, Toshiba, Gateway, etc.).
(2) Strangely, they all seem to have 16:9 aspect ratio (the iPad is 4:3). OK, that's great if I've got a widescreen movie, otherwise...? I think it's a pain.
(3) Android tablet? Then I think hardware is a BIG DEAL. I currently have the Pandigital Novel, which runs Android 2.0. There is talk of getting it up to 2.1, and maybe even 2.2 (good luck!).
The last point is where owning a fancy Android phone can set your expectations, in at least a few ways. First, the Pandigital and many other tablets around $200 have a capacitive screen, which means multitouch is a problem, and the general user experience is nothing like, say, a Droid.
Second, I think a tablet will need a dual core CPU in order to feel like a good Android phone. The video reviews I've seen of the low-end tablets all look the same...very sluggish, and not good for multitasking. And likely also problems playing back HD video (which is a reasonable thing to ask of a 7", 8", or 10" tablet).
Conclusion? I say give it a few months. The market is really churning right now, and I GUARANTEE you that if you buy something before Black Friday, 2 weeks later you'll see something better and wish you'd waited. That's always true with consumer electronics, but ideally you should get to enjoy your purchase without buyer's remorse for a month or two!
Oh, here's a GREAT list of upcoming tablets at androidtablets.com:
List of Upcoming 10" Tablets
-Matt