Microsoft is buying DATAllegro for, in essence, its data warehouse scale-out technology. And guess what? DATAllegro relies on Infiniband. The last time I looked, DATAllegro's Infiniband supplier was Cisco.
Googling around, I get the impression that Microsoft has been up and down with Infiniband. First they sponsored Infiniband. Then they pulled back in 2002. But in 2007 and 2008 Microsoft has been talking about partnerships of some kind with small Infiniband providers.
All that said: Microsoft/DATAllegro will surely support many more hardware/storage/networking configurations than standalone little DATAllegro now runs on. Not all of these will include Infiniband (think 10GbE). And not all the Infiniband will be Cisco.