It's actually been a couple of days, but I am just getting around to announcing it.
Mozilla Messaging now has it's own planet, planet.mozillamessaging.com, aggregating blog feeds from various Thunderbird sources. It's a complete ripoff copy of Planet Mozilla, just with different feed configuration.
It should get redesigned at the same time as the next incarnation of our main web site, so pay little attention to what it actually looks like, and just subscribe to the feed already.
Cheers.
P.S. If you feel like your feed (or a feed you like) should be on there, file a bug asking for it to be added