I think what you mention above are common bugs with multi-GPU systems. It isn't a trend. I've had similar things happen to me with SLI. What I disagreed with is the notion that seemed to be there that this was a routine
with Crossfire or 5970 and not an anomaly as if there were some kind of architectural deficiency with the card as compared to Fermi.
I benched lots of games over here and never saw minimums on any of the 4xxx series Crossfire setups dip below what a single GPU did. In most cases there was 70+% scaling.
I also provided frapslog recordings to go with it so there was no doubt. Granted I haven't done this with the 5xxx series yet, but I find it hard to believe that Crossfire's regressed since that time.