I haven't seen it mentioned anywhere, but there is now a
Glyph of Ferocious Bite (click the link to see it) that prevents the extra energy consumption, turning it into pretty much a clone of eviscerate. This is something that I personally always wanted throughout WotLK, but Cata will fix FB scaling so that using 100% extra energy will equal 100% extra damage. I just wondered what the thoughts are on the glyph. It could make it much easier to weave FBs in without completely destroying the rotation. It also makes FB is a good CP dump during berserk, although again, not sure how the new scaling will affect things.