One blogger polled more than a dozen other bloggers to get their take on this question:
"If you are drawn to write on a broad variety of topics (3-5) even if there is a remotely common thread, are you better off doing it on a single blog or creating several niche blogs for each one?"
There was an interesting range of opinions. On one level, the opinions seem to break down according to whether the bloggers are writing blogs for business purposes or more for personal motivations.
The business bloggers tended toward writing narrower niche blogs. The personal-interest bloggers tended to favor combining a broader range of topics under one blog. To some of these personal-interest bloggers it wasn't about blogging on a particular subject, so much as it was about sharing their voices or developing a personal connection with readers.
That's not surprising when you think about it.
Consider what the reader expects and wants. On personal interest blogs the reader is more likely reading for a combination of personal reasons, including, in part, entertainment.
For business readers, it's more about searching for specific information or staying up to date on a particular topical area. To attract and retain business readers, they expect some level of consistency of what they'll find on your blog.