It won't be any time soon. While an OFED stack is available, it is incomplete and the drivers suffer from performance issues.
Yes, but Average Latency would still be a lot lower than ethernet and since the
OFED Stack is underlying between the hardware and software layer, so latency is still in the micro second range
Throughput will still be noticeably more even with a botched OFED stack, however that can be tuned as we go along specially if we show interest in it, it will eventually get the support it needs / deserves as noted before its A LOT cheaper than 10GBe.
Your average dual port infiniband card can be found as low as $35 on ebay, and there were a few complete setups ( switch, 24 cards and cables ) starting at $500 where you'd pay about that for a 10GBe network card alone and you still dont have a switch and still need at least another card.
I'm hopeing for the same idea to be implemented in pfSense 2.2 as its going to be based on FreeBSD10