Yep, just for reference I just hit this too. Try to run the KVM portion of the intel remote management module 3 on a server class chassis, and I get jviewer.jnlp loading in gedit.
Also F16 and also x86_64 (though I doubt arch has anything to do with it). It used to work ok on F14. Aggree its probably missing the association. icedtea-web-1.1.4-4.fc16.x86_64 is installed.
Update: got it going by installing the oracle JRE, editing the jviewer.jnlp, fixing the target servers IP address (was missing a decimal place) and changing the protocol from https to http, then running javaws /tmp/jviewer.jnlp Probably the file editing is because of bugs in the intel software, but I just put it here for anyone who lands on this thread looking for rmm3 info.