The grip does 3 things - and it does them very well:
- The entire ergonomics of the somewhat small body of the t2i are much more comfortable. The grip adds weight which balances out larger lenses as well.
- Extended battery life X2 as it fits 2 batteries.
- The grip includes a side button for vertical shots common in portrait work.
So.. the new t4i is here. As of now, I see no real reason for me to consider it, as I doubt it will have a substantial increase in IQ for stills. The only reason I would consider it is the improved AF, however that too may be trivial for my style of shooting, which is stills, using the center AF point only.