if you got hit by Panda and have multiple sites:

[DesignerRamsey]

Did it hit more than 1 site?
If yes, was it the ones with the most traffic?
Are they under the same AdSense or Webmaster Tools account?

I am wondering if they are targeting "accounts" and multiple sites within the same accounts.

It's a theory - but the 2 main sites I had in my account both were deeply affected by the Panda update - in a bad way.

Others I know had multiple sites hit - same thing - under same account.

[Jeff Hampton]

My understanding is that the algorithm itself does not target accounts.

If you dig deep enough, you may find that there were commonalities that would have caused the sites to be hit, whether they were in the same account or not (same type of backlinks, same themes, etc.)

But if there's no commonalities, it could be due to triggering a human review.

As for whether your sites were hit as a result of Panda, it may not matter, but:

"Panda was just one of roughly 500 search improvements we expect to roll out to search this year. In fact, since we launched Panda, we've rolled out over a dozen additional tweaks to our ranking algorithms, and some sites have incorrectly assumed that changes in their rankings were related to Panda." - Amit Singhal, Google Fellow

[masterjani]

Actually the algorithm change might affected your sites.It is not because whether it is from same account.
Check for duplicate content and url structures,keyword stuffing etc.Also check whether any messages in webmaster tools about the hit.