I received my replacement motherboard from NewEgg (they were great about it) and got it installed without issue.
What I noticed is that the UEFI (BIOS) version that came installed on the B3 replacement board is 1408. I was running 1204 on my original.
Like all things new, I wanted to make sure that it was the "latest and greatest" so I went to Asus support site to check for an update.
Here's where I get confused.
All the original updates up to 1204 (the one I was using) were there, plus a 1305 and a new 1502. The site does not list the 1408 that is currently installed and that it came with. I do not see anything on the site that would indicate a difference between the original (B2) and the replacement (B3), so will the 1502 work, or should I just leave well enough alone and stay on 1408? The notes for the update don't indicate that there would be much of a benifet.
On a side note, the system is working much better. The keyboard and mouse issues within UEFI are gone, memory issue went away and was able to one click OC to 4.3 stable.
asantesoul's advice is good ... when a board has been out for a while and all the niggling little bugs have been found and eliminated. The boards for Sandy Bridge are still new and haven't yet been perfected, and will get faster and more stable with future updates.
I suggest keeping up with the newest UEFI/BIOS updates until the end of June or so, and then after that you can stay with a good version that works for you. By then they should have most of the bad stuff worked out.