It always returns true, no matter which key combination I use. I tried with other key combinations, such as Ctrl+Shift+J, Ctrl+Alt+J or Ctrl+Alt+R, for instance. The only difference is that with the last one the following message is printed in the console:

Qt Code: 
  1. X Error: BadAccess (attempt to access private resource denied) 10
  2.   Major opcode: 33 (X_GrabKey)
  3.   Resource id:  0x5d
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So Ctrl+Alt+R is already grabbed by another application but the former key combinations aren't and they still don't work. :-( I have openSUSE 10.3 with X.org 7.2 here but I've also tried in openSUSE 11.0 with X.org 7.3 and got the same results. Key grabbing works in my system, as I have Yakuake here and whenever I press F12 it opens as expected.