The 900 is a great case.
As Andrius pointed out, the Twelve Hundred is coming out soon, and is basically the nine hundred, except that it's a full tower (vs the mid) and has a few other features.
If I were buying now, knowing how well the nine hundred does, I wouldn't hesitate buying it either.
It seems as if they updated some of the things about the nine hundred
- the twelve hundred - is roomier
- the twelve hundred - has 12 drive bays (vs 9 in the nine hundred)
- the twelve hundred - has fan filters (less dust)
- the twelve hundred - has 3 120mm fans on the front, 2 120mm out the back, and the 200mm fan on the top.
- the twelve hundred - has holes in the back plate (where the motherboard connects) to allow for better cable management (you have to mod the 900 or get creative)
The 900 is still great, just smaller - only 2 front fans, 1 back, and the top 200.
Either is a great choice.