I just released my launcher (updater) that I use in my game, details here.
Woot woot 
I’ve had no problems with webstart as long as you don’t allow offline mode, which for an online game is fine :). Sometimes web caches get in the way, but you’ll get that whatever technique you use if you do it over http/ftp. Some proxies also ignore the cache TTL headers, which is annoying.
Endolf