5) The Erdmann Nexus, by Nancy Kress: magic in old people's home, which turns out to be related to Arthur C. Clarke's Childhood's End, only not quite as good.
4) True Names by Cory Doctorow and Ben Rosenbaum: post-singularity stuff which made it rather difficult for me to care about the characters. Also dubious measurements.
3) The Political Prisoner by Charles Coleman Finlay: nasty story about nasty people (with surprisingly few sfnal elements), but very solid and coherent world-building, both in terms of human and physical geography.
2) The Truth by Robert Reed: also a nasty story about nasty people, but very well worked out procedural of US agents interrogating a suspected time-traveller who has been involved with horrible terrorist atrocities.
1) The Tear by Ian McDonald: takes a premise which is quite similar to the Doctorow/Rosenbaum True Names but does it much better: believable characters (several of them inhabiting the same body) and wonderful descriptive language of a richly imagine future very different from ours. Solidly gets my vote.
Interesting that my two first choices so far (The Tear and Anathem are the only nominees in their respective categories which aren't in the WorldCon ebook package. No doubt we shall be chewing over the impact this has on the results come September...