I just got a Nook Color, $250.00. Here's my impressions:
1) Out of the box, this makes a fairly good ebook reader. I previously owned the older Nook, and when I registered this one on my account all my books showed up. (Actually, I couldn't download them immediately -- I had to update my credit card number my B&N account, as the previous number was expired. This is because they use the CC as part of the DRM scheme).
PDF viewing: kind of so-so, took me a bit to figure out how to turn pages. Turns out that you swipe to scroll the page up, then the next page shows up. This is different then the native EPUB reader app, where you either tap-to-turn or swipe across). Also when you have the document zoomed, there is no way to lock the left-right panning, so whenever you swipe upwards to turn the page the document can become off-center again.

Web browser: Functional, I think it is the standard Android browser.

Hackability: Although not supported, you can easily modify it to enable adb support, to allow for side-loading Android apps. This is where I think it is neat -- all you have to do is make a micro-sd card with a boot loader / fs image, and it will automatically boot from the sd card upon power up. Apparently this is hard-wired in, so this means that future software updates won't be able to disable this feature. So rooting consists of downloading a boot image from nookdevs.com, which contains a small Linux rescue image along with a boot script which modifies the OS initrd image to turn on adb support.
There is also floating around a complete Android 2.2 image that you can write to an sd card and run it without otherwise modifying anything on the Nook.

How it performs as a tablet (hardware wise): The screen is very readable, high res and low glare. CPU: 800 mhz. Has wifi, but no bluetooth (apparently there is a bluetooth chip in the device, just no driver for it [yet]), no camera, no 3g, and no user-replaceable battery. Also the micro SD slot is kind of hard to use (you lift a cover on the lower left corner, but the framing around the beveled corner prevents you from getting a good grip on the SD card to slide it into the slot -- not the best design I've seen).

Overall rating: not bad for the price. If you hack it to enable full Android support (including app store), then you have a decent Android tablet. If you don't feel like hacking it, then B&N is supposed to be releasing an update within the next month or so, which brings it up to Android 2.2, and gives you a choice between the B&N home screen and a standard Android launcher. Not sure if they will enable the Android market (Google requires a cell phone, among other hardware pieces). But hopefully they will let you side-load Android apps.