something simple.
My shifter also felt loose. It never tried to pop out of gear but it was definately loose feeling.
I poped the boot off the shifter and you know what I found.
The upper part of the shifter tower is held on with 4 bolts. Mine was missing 2 and the other 2 were loose. I snugged them down and the problem went right away. Now I just need to get two more. I think they are metric since most everything else on the car is.