Kindle Kaves

Amazon announced late Friday that the company is modifying systems to allow authors and publishers to decide whether to enable Kindle's text-to-speech function on a per-title basis.

[from CNET] Amazon retreats on Kindle's text-to-speech issue
"Kindle 2's experimental text-to-speech feature is legal," Amazon says, but "We strongly believe many rights holders will be more comfortable with the text-to-speech feature if they are in the driver's seat."

So Kindle's text-to-speech will depend on each publisher and title; some will have it, some won't.