Like Taras, I think planet.mozilla.org content should be related to the Mozilla project.
Personally I like reading other community members' non-Mozilla content, but I recognize that many (most, probably) other people expect planet.mozilla.org content to be Mozilla-related (regardless of fine-print disclaimers) and I think that's a reasonable expectation. Looking at it slightly differently, Taras' request for an aggregated feed of Mozilla-project-related posts is very reasonable, and planet.mozilla.org is where people will start looking for it, so that's where it should be.
FWIW, after migrating from Moveable Type to Blogger and discovering that gave me the ability to send only Mozilla-tagged posts to planet.mozilla.org, I did just that, starting in January. If you want to read my non-Mozilla-related content, please subscribe to my blog feed directly.
I'll be writing something there shortly about my ongoing holiday in Europe. Currently I'm watching rats run around Fontaine des Innocents in Paris :-). And wondering why my Android phone suddenly can't connect to a WiFi network it was connected to an hour ago, which my laptop is using just fine :-(.