I posted a review of James Tiptree: The Double Life Of Alice B. Sheldon at my blog. If you haven't finalized your list yet, please consider adding this one. If you HAVE finalized your list, sneak it on. This is an excellent biography. No kidding.
This was on my list (coming soon!) for the Challenge, and I truly meant to hold back from reading it until 2008, or at least the waning hours of 2007, but I just couldn't.