(Coming to this late, but ...)
I have been informed via my editor at Ace that Amazon is having a major ebook push in October. This has fed back into requests for hitherto unavailable titles (in ebook format, at least), and two of my books that Ace's ebook people were sitting on the rights to are now in the process of being converted into ebook format as part of their response to Amazon.
This is just one data point, but it strongly supports the speculation that Amazon are going to shovel out a whole lot of original content on or around October 15th, which in turn supports the possibility that the Kindle is likely to launch around then.
As it happens (by sheer coincidence
I have a speaking engagement at Amazon HQ in Seattle on October 9th. If I get the chance I'll do some digging and see what I can learn (and see if it's possible to get my hands on a Kindle -- it's a long shot, but you never know).