Why not simply 1 blog with appropriate tags on your posts?
Personal, Professional, Technical, Speculation, Announce, Startup, Rant, Meta (blogging about your blog).
You could even derive versions of your blog based on those tags, for example one with (and Personal (not Professional) (not Startup) (not Technical)). So you could have 4 sites: the one with all tags available, and 3 others with restricted tags (that the user can restrict further). This way you can direct someone to your Technical blog without them tripping in your Personal stuff.