Yes, the new 1.5.20 cygwin dll has been released and thus also the official qt3 package should be working.
I also noticed that, but I did not try to remove your uic.exe etc and try.
There are no big issues with both 1.4.x and 1.5.x. They have the same exact functionality as on *nix.
After 1.4.2 is released, I will try to draft a proposal to cygwin-package with 1.4.2 as official and 1.5.x as experimental. Bo