I might have forgotten all details, but as far as i know the HK G-11 was technically a success, when cook-off issues had been solved.
But political issues during the re-unification of west and east Germany didn't allow for any large scale acceptance of the G-11.
The concept of caseless ammunition is sound of course, but the development and acceptance of it isn't as easy...
The US is currently working on caseless ammo on the LSAT program:
http://www.dtic.mil/ndia/2009infantrysmallarms/wednesdaysessioniv8536.pdfWhat i find really intriguing on the G-11 is the rotating chamber and that when in burst mode the cyclic rate is extremely high, around 2000 rpm and for a 3-round burst there will be just one recoil impulse.
Sad to say i've never handled or shot one, yet..