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.
Is there--understand, here, that I don't have a blog and haven't blogged, so I have no idea--is there blog software that will do this for you already? Like, handle a different URL, css styles, etc. but point to the same database? That sounds like it would be really handy.
I liked the title, but the key points of the post kinda broke down into very boring and obvious practical matters.
I thought a more interesting point to make would have been to say that you need 3 personal blogs, for some reason or another. Now that'd be a nice, juicy, meaty controversial statement to make.
I have 3 blogs, i have one in Bulgarian in witch i post everything im interested in, i have an English version of it, and a 3-rd blog where i post the cartoons i draw. Im lazy and don't update my English blog very often, and i haven't drawn anything in two weeks.
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.