I have made a group and modified it to shake but it immediately moves up several inches in the z direction and the hot spot is left behind and cannot be centered. Bug? (Carrara 6)
That's what the shake modifier does, it moves objects (in this case a group) about the hotpoint.
If you press play on the timeline you will see it jump around.
Keep the amplitude down and the rate high to get a more believable look to an animation. Personally I dislike the shake modifier as the jumps are not smooth.
It's actually pretty easy to build a convincing shake using the graph editor instead.
I figured the shake had taken the group a jump but with 0.0 inch amplitude, that is not right. When I use amplitude 0.5 in. on a group it sometimes shakes the right amount. Then I add it to another group and it makes the crazy jumps of nearly 6 inches!
I assume you mean by "graph editor" to manually move the group up, down, around, etc. in small steps? That is pretty tedious. Do you mean something else?
The graph editor allows you to go in and edit the values of keyframes directly.
Yes you will need to set some motion keyframes but that's pretty easy. It should take a couple of minutes to get 30 or so keyframes in place, then with the graph editor you can change the values by a random amounts each time and directly edit the curves between values.
Should take ten minutes tops to get a decent result on all thre axes. (You only need to translate on one axis to get keyframes for the three which then can all be edited)
Ok it's not as quick as just applying the modifier but as in all things if you want to produce quality you have to put in the time and effort. Plus it's actually fun and gives you total control. The thing is once you've done that, you can switch back to sequencer mode and treat the keyframes like any others. Make a set of loops that you can drop into the timeline wherever you wish.
By the way, you're right about the group thing being odd, I rarely use shake and only then directly on an object so I never noticed that the modifier displaces the group on the Z axis. So possible bug report?