trace attached...
Created attachment 96712 [details] trace
You need at least version 2.14 of gnome-base/libgnome, do you have that new version? gnome-power-manager has the check for libgnome too lean. Filed upstream as http://bugzilla.gnome.org/show_bug.cgi?id=355437 The dependency in the ebuild is wrong too, hence you probably don't have new enough libgnome installed yet. Is that correct?
libgnome dependency fix committed to CVS. Should propagate to sync mirrors shortly. Please reopen bug if >=libgnome-2.14 doesn't solve compilation problems. Thanks for the report!
Whoops, forgot to close bug