I use this alot with my druid... it comes handy in many situations, examples:
- Lurker Below in SSC, if youre dpsing, instead of running away from whirl what you can do is shift to bear like 1 sec before whirl (considering you have furor, if not then shift a bit earlier so you can build a little rage by hitting him a few in bear form) then let him whirl you and spam the feral charge button til youre back on his ass -> shift back to cat form.. (since shifting is instant now , the sequence is like: "dps in cat -> 1 sec before whirl -> shift bear (no need to shift out of cat, just click the bear button) -> spam feral charge button -> back on him -> shift back to cat -> resume dps"
- Another example is Lady Vashj in SSC, she does her rooting crap every now and then, its kinda same situation... "rooted -> bear form -> feral charge -> cat" and watch the rogues/warriors whine

P.S. we usually have a druid tank her since they can do the above.. easier than having to spam BoF on a warrior...
For PvP i like feral charging the hunters when they wing clip/cons shot me.. sometimes i even bash them if they make me angry, then shift into cat and resume dps...
oh and the cherry on top -- potting while in forms (kinda

):
/cancelform
/use Master Healthstone
/cast Cat Form
^ saved me lots of times both in pve and pvp...
replace Cat Form with Dire Bear Form for your bear needs.. and HS with your favorite pot...
anyway, just my 2 cents =)