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 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:

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.