Given SandyBridge arriving soon, Intel's current woes, etc., is this a good time to get a Rev.D. MP with a hexacore? A "bad time" would be that there is something coming within the next 3 months.
Nobody knows for certain, but alust2013 is probably right. I don't believe the Sandy Bridge version of the Xeon has been released and the multiprocessor versions of the CPU aren't due until much later in the year. I doubt Apple would update the single processor MPs independently of the dual processor MPs. Buy away.
LP implementation is more than vague at this point (I don't expect early implementations before 2013), FW3200 is dead, and the MP already supports USB 3.0. I've got it in my Pro.
I actually don't really know what you're talking about, I suspect you mean SSD storage, though.
Given that the Mac Pro features upgradable hard drive bays, SSD's have never been a problem in the Mac Pro. You can even get them directly from Apple via BTO.
However, the reason why there won't be any upgrades till late this year, or early next year (which is what I believe too), is the fact that suitable Sandy Bridge CPU's for the Mac Pro won't be available till then, and there is certainly no reason for "upgrading" the machine with the same processor line we've got today.