What's Old is Now New
First of all, Forgeworld has issued some updates for the Corsairs as part of their 6th edition updates, but they are not released as part of a single update. Rather they were released piecemeal by subject. You can find the updates here.Note that you will have to download a bunch of pdfs; one for the Shadow Specters, one for Iryllith, one for psykers and one for vehicles, to name a few.
The good news is that no 7th ed update is required, so you should be fine with the book and the pdf updates linked above.
The bad news is that Corsairs don't get Ancient Doom or Battle Focus! If you are an Eldar player you know how important Battle Focus is these days. Being able to run and shoot (or vice versa) is a vital strength.
More good news comes from Army Builder; their Corsair list has been updated so that their equipment and wargear follows the convention established in the latest codex. Thus, lasblasters get 3 shots, shuriken weapons get bladestorm, shimmershields grant a 5++ save all the time, and so on.
So while the individual models may have lost Battle Focus, at least the rest of their standard eldar equipment works the same way as their Craftworld kin.
Incompatibilities
It's not so rosy for the unit entries in IA11 that mimic their craftworld cousins, though. The rules for falcons, serpents and other units pulled directly from the main eldar book list their rules explicitly. Thus a rules-lawyery player could argue that you have to use the 'old' rules with your corsair models rather than the updated versions in Codex:Eldar.My first answer to this is; don't play with this person.
My second answer to this is; Night Spinners. While the new monofilament rule is interesting, I much prefer the old lock-every-unit-in-place-until-they-make-a-dangerous-terrain-test version, even with the lower strength. Even knowing that dangerous terrain tests allow for armor saves now! I'll take twin-linked barrage over non-TL every time.
My opinion is that anything that has a counterpart in the main eldar codex should mimic the rules presented therein rather than the IA11 rules. That way you don't have two different kinds of wave serpents or harlequins or falcons on the table. It's simpler and it makes sense.
The Good, Bad and Ugly
Despite the fact that the statline of your average corsair now suffers a drop in WS and Initiative, I don't think the corsairs have fared badly. For one thing, they have access to the Craftworld Outcasts. This means you can bring a squad wraithguard with D-Scythes as elites and have your Corsair Prince grant them Deep Strike. If you have no-scatter deep strike tricks, so much the better!The Nightwing Interceptor is now the best flyer in the game. With a 4+ cover save all day long, bumping to 2+ if they choose to jink, they are capable anti-air fighters and can hunt down monstrous creatures with ease. They are also cheaper than the crimson hunter.
Corsair jet packs got a bit of a bump too with the 2d6 jump move during the assault phase. Of course with Battle Focus it would be even better but oh well!
In short, I think the Corsairs have gotten a tad better since they first came out, and you can expect to see some news of my progress with my Umbral Shrike warband as I dive back into hobbying once more!