Maybe i'm a total newb by asking this question as it may already be there, but maybe we could add a function that adds units to a particular group. For instance you have a group of 2 flash. You want to add another 3 flashes. Maybe it would be easier if you could just select the 3 flashes and press CTRL + SHIFT + 1 which adds the 3 flashes to group 1. The same goes for CTRL + ALT + 1. 5 flashes in group, select 3 of them that are in group 1 and press the combo shortcut and they are removed from the group. I think it might only give a small advantage over the normal way to do it. Press 1, select with Shift the additional flashes and press CTRL 1, but this way you don't have to preselect the existing group of go and find em which will draw your attention away from more important things.

also, when making a factory part of a group (making every unit it builds part of that group to) ignore the factory when giving move/attack orders etc. to the group (as it was in OTA)

Related topic:
http://taspring.clan-sy.com/phpbb/viewtopic.php?t=1385