I've fiddled a bit with Planet before; if there's no objection I'll set that up later today. If anyone wants in, let me know where to find your blog. :)
No objection from me, but: I want us to make sure that all the blog posts appearing are only Wikimedia-related. So I would insist that blogs either provide a Wikimedia-specific feed, or that we are able to filter them on our side by tag.
Oh, I don't know; Sometimes you get some interesting stuff that's not strictly MediaWiki / Wikipedia / Wikimedia - related.
For example, you might miss out on stats about the number of people that fake their identity online ( http://wikiangela.com/blog/a-sad-loss/ ) , videos of suburbs being hit by asteroids and zapped by aliens ( http://leuksman.com/log/2006/06/17/video-crap/ ), and maybe at some point a posting about the OLPC's security architecture ( http://blogs.law.harvard.edu/ivan/ ).
Isn't it nicer to have something organic and freeform and inclusive and alive, that flows in unpredictable directions like a good conversation, rather than something that's narrow and exclusive and walled into a small box?
I say: embrace the weird and the wonderful and eclectic in all its forms, and let the chips fall where they may - the only criteria should be whether MediaWiki (core or extensions) / Wikipedia / Wikimedia / wikis-in-general are a major personal or professional interest to the author, and then wiki-related stuff will just naturally tend to form a large percentage of the planet's content (although it will include other stuff too). You see this pattern already in other planets (e.g. Planet Debian). Or at least maybe try that approach at first, and if it doesn't work then refine it from there.
All the best, Nick.