One thing I've noticed now that I've been playing with the range argument is that arguments with xyz coordinates in them HAVE TO use absolute values. As in, you can't specify "~4 ~1 ~2" to mean "4 blocks away on the x, 1 up on the y, 2 away on the z". The only reason that bugs me is if I want to use an external map editor to copy and paste a structure a bunch of times I have to reprogram any command blocks in it that use arguments with xyz's. With relative coordinates you don't have to worry about that so long as facing is maintained (south is still south, east is still east, etc).

To reproduce? Start a single player game with creative mode and cheats on, use "/give @p 137" to get a command block, stick a button on it while crouched, program "/effect @p[x,y,z,r=1] 21 5 3" (replacing the x y and z with real numbers of course). Press the button while standing at the coordinates or beside it (should be JUST the coordinates since it's range 1 but that's a seperate bug report) and it should give you Health Boost 3 for 5 seconds.
NEXT, replace the coordinates with "~1,~0,~0" stand at the new spot and press the button. Nothing will happen (because the command block syntax-errored) and the "previous output" window on the command block should say that ~1 isn't a proper number.
For an example of a command block NOT choking on relative coordinates, try "/tp @p ~4 ~2 ~4"