here's my take:
twombly essentially gutted the following language of conley: "a complaint should not be dismissed for failure to state a claim unless it appears beyond doubt that the plaintiff can prove no set of facts in support of his claim which would entitled him to relief.” (i don't have my textbook w/ me, but the majority did this by holding that the mere allegation of parallel conduct is not enough.... etc.) so, arguably it turned rule 8's notice pleading requirements into a fact pleading requirement.(similar to rule 9 for negligence)... so twombly adds an additional “plausibility” requirement of fact pleading. it's unclear whether this new pleading standard applies to all cases, or only expensive/anti-trust cases. in theory, this "new standard" will lead to more successful 12 (b)6 dismissals.
i agree with (i think it was) Justice Steven's dissent. just my thoughts.