Kissinger,
From my experience in using grids as child record entries. (I use them quite substantially against all recommendation), the 2 areas that needs special attention are:-
1) Valid events. Users CAN FAIL a grid column's textbox valid event and EXIT to another control. Hence it can never safely trap invalid values.
2) Delete line in grids. When there's only 1 record in grid, deleting won't make it disappear if u set the grid to allow auto addline unless u somehow move the records!
Best of luck!
Yau