So my attempts at using C# floundered mainly because I only have Mono on one box, whereas I can get Java easily on all three.
In fact I can get many versions of Java! (Sun JDK 1.4.2, 5, 6 (Mustang), sablevm, kaffe and gcj 3.3 and 3.4).
I've also been trying out a few desktop Java apps: Azareus, RSSOwl (which is better than BLAM! 1.4.x), Sun Download Manager and QNext. The former two are brilliant, the latter two, just "OK". QNext offers a lot more than Gaim but only if you need it and I don't.
I've also built Scarab (a server app) using ant, which was painless. Thank god from jpackage.org!