Update: Matt Cutts of Google notified me these are not Panda notifications. I still do believe these are new notifications, just not Panda specific. Matt commented on this below and tweeted it. John Mueller from Google said on Google+:
We send out a lot of notifications, I wouldn't necessarily see them as being limited to any single change / penalty / algorithm change. The goal is usually not to identify specific algorithms, but rather to help the webmaster to improve the quality of the website overall.
In this particular case, it was automatically sent at some point after an initial manual review (Matt talks a bit about the differences at When are penalties lifted? ). There are some messages that are more automated (eg outdated CMS version alerts, malware, etc), and others that need more manual input, so it's not really possible to generalize based on this individual message. It's great seeing more feedback flowing to webmasters, and I'm also happy to see that these messages can help to guide the discussions on the forums.
We know Google has seriously ramped up webmaster communication, so when I saw a Google Webmaster Help thread where someone received a notification about their pages being "low-quality," I was not surprised.
The message read:
We've detected that some of your site's pages may be using techniques that are outside Google's Webmaster Guidelines.
Specifically, we detected low-quality pages on your site which do not provide substantially unique content or added value.
That sounds like a Panda notification to me!
Almost 9 months ago, I asked Google to send webmasters Panda notifications and it now seems they are doing so.
Google has not confirmed with me on the record that this is indeed a Panda notification but I am told this is a newish notification being sent to Webmasters via Google Webmaster Tools.
So if you think you site was hit by Panda, I guess this message might confirm it for you.
Forum discussion at Google Webmaster Help.