For mods… eventually DownloadService and/or FileOpenService and/or signing and open/load the usual way.
@ sillysoft
One of my needs is for people without java installed to be able to run it.
Well, they also need an operating system, drivers for their graphics card, drivers for their soundcard…
So… dunno… “visit java.com and download the Java runtime environment” isn’t that difficult. I mean… seriously… not everyone out there is totally retarded. Everone who’s able to download your game is also able to install the JRE. The “difficulty” is the same.
@moogie
I feel your pain :-/
@Kev
Chris hinted that sun is planning to do something like that (eventually), but as an applet(?).
@Adam
Over at JGF should be a small html file with links to all jnlp files (for c&p it into webstart) 
Hmm… let’s see… what makes webstart not so perfect (so far):
[]Use of modal (blocking) dialoges with null as parent - d’oh.
[]No intuitive way of preventing updates. Update? Yes, No, Always, Never.
[]No pause/resume toggle-button at the download screen and no resume in general.
[]The silly message (should be more like the messages you know from a browser - eg without that ~we from sun think that this guy isn’t trustworthy caugh crimminal caugh and that he’ll most likely blow up your machine! No Shit!). Of course it’s ok to warn the users, but there isn’t a need for overdoing it.
[]There should be a way to make applications persistent. That means moving it out of the cache.
[]There should be a way to organize the applications.
[]Certs should be cheaper 
[]… (bitmask) transparency behaves somewhat strange on win9x [only transparent if selected?!]… well ok that doesnt really matter.