There is no information on specs, though it will probably be a mid-range, mid-priced device. The OS version that will be used isn't mentioned in this story either, but I would expect it to be something below Honeycomb given the tighter control that Google is maintaining over it's use. There is mention of touch screens already being secured for this tablet so there hopefully won't be any Transformer type component shortages to slow production.
The PCWorld article covers the less certain rumors that the OS will vary so drastically from stock Android as to be unrecognizable. I've read this rumor before and looking at the work that Amazon has done on their existing Android applications it does make sense. When you are using the Cloud Player or Kindle apps on your Android devise the look and feel is very unique. I don't think it is much of a stretch to assume that their tablet will be no different.
The Nook Color runs Android, but unless you knew that going in you'd be hard pressed to figure it out on your own by using the device. The coming Android based tablet from Amazon may well be a stock OS, but the money bet is on a customized version of Android that Amazon can call it's own.
Amazon really isn't interested in selling you the best Android tablet available, they are interested in selling you the best device that ties in to all of their available services. Amazon is in a position to settle for less profit from the device in hopes that the content that you rent or buy to consume on the tablet will come from them.
Going by this report we should see shipments of the device in the second half of this year with back-to-school season being my guess.