You don’t need 1 blog: you need 3.
47hats.com
47hats.com
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.
edit: "67bigones" looks like it's available, too.
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.