As far as electromagnetic shielding and such, I've no clue. :?
When working at radio frequencies (RF), you definately can get strange results. I did some tests a month ago where an anodized chassis acted much different than a nickel plated one (both aluminum) in the same test setup. Since the anodized surfaces weren't conductive, the RF energy radiated from the enclosure very differently.
So grounding issues are the less 'magical' problems I understand. An oxidized ground lug, for instance, could give you hum fits on an old chassis. That's one neat thing about the blue board, as the ground plane is all on the PCB.
The more pragmatic reasons of steel vs aluminum are well stated in another thread here. I think Ed has won me over, though, and I'll start using a steel chassis more often, if only to support the 60W OPT of the Eiclone. I just hope my Unibits hold up! :) Cutting oil suggestions anyone?
Shannon