Free Safeties lose value because they dont get the chance to come up and help with run support as much as a SS would. Now there are always some FS that are good IDP picks due to either their outstanding athleticism or a defensive scheme that moves him into the box more often.

I think Huff will lose tackle opportunities, but he will be able to go back to being the big play back he was drafted to be. He should see more INT chances and will move into the box on certain downs. So in conclusion, if your league is standard scoring for IDP, then he will lose some value, but if he can take a few INT's, it shouldn't be a huge drop.

I agree...

I also think Huff is still on the upswing in terms of NFL development, now entering his 3rd year and having just turned 25.  So I expect that natural progression to also help offset any decrease in productivity due to moving to FS from SS. 

Plus, with two very dominant CB's in the Raiders backfield, Huff won't have to spend as much time assisting them with coverage as many Free Safeties.  Hall and Asomugha are both very capable of single man-to-man coverage, which will leave Huff open to come up to offer additional run protection, even at FS.

Most defenses don't have that luxury.

I picture Huff as more of the old "roamer" type back -- where he will be able to emphasise the "Free" part of "Free Safety".