I (admittedly) don't know much about Infiniband. I know what it is, but I just don't hear that much about it and have not used it in my experience. Well, it looks like Sun is taking a gamble on it.
Sun touts many advantages of Infiniband vs. Ethernet in the race for the unified network. Infiniband is poised to beat Ethernet to the 40Gbit/sec mark and products are expected to have latency as low as 60-70 nanoseconds.
I'm going to have to agree with quotes made in the EETimes article and say that Ethernet advances may be slow going due to IEEE red tape, but Infiniband just doesn't have the market share that Ethernet does and data center managers are looking to reduce the types of fabrics, not increase.
Check out the EETimes.com article here