Mixing topics in a blog

I was reading this Jakob Nielsen Alertbox about the top 10 weblog design mistakes. Mistake #8 was:

Mixing Topics

If you publish on many different topics, you're less likely to attract a loyal audience of high-value users. Busy people might visit a blog to read an entry about a topic that interests them. They're unlikely to return, however, if their target topic appears only sporadically among a massive range of postings on other topics. The only people who read everything are those with too much time on their hands (a low-value demographic).

The more focused your content, the more focused your readers. That, again, makes you more influential within your niche. Specialized sites rule the Web, so aim tightly. This is especially important if you're in the business-to-business (B2B) sector.

If you have the urge to speak out on, say, both American foreign policy and the business strategy of Internet telephony, establish two blogs. You can always interlink them when appropriate.

It makes sense but I'm assuming this is only meant as a guideline and not a hard and fast rule. My question is: Is mixing topics ever the right thing to do? And if so, when? Do you know any blogs that managed to pull it off?

Answer

It depends on what your blog is trying to achieve.

I agree with this much of your quote: readers come back most consistently to a blog that is focused, that offers one thing consistently. The reason is that, the more you switch around the key element of your blog posts, the less likely each individual post is to be enjoyed by a regular reader.

But two important provisos to that:

The consistent element isn't necessarily a topic. Some people have great voice or wit or style, and that's what keeps readers interested - and coming back. Or they're just really great at continually finding new interesting things. Or, they've achieved celebrity status and have fans for whom the fact that that person is writing it is the element that interests them. Scalzi's Whatever is a good example, with probably a mix of all the above.

And secondly, some mixture can be excellent - it gives you a specialty. For example, writer blogs are a dime a dozen, but some writers stand out because they write about writing and one or two other things. So Jim Van Pelt blogs about writing and about teaching, and Mette Harrison blogs about writing and running marathons. I'd probably never go looking for blogs on education or marathons - but reading about writing and those things gives the blog character and uniqueness - and I follow those blogs devoutly.

So in summary, the advice not to overscatter yourself is quite correct - a key of publicizing anything is to choose your target audience, and then target 'em like heck. But that doesn't mean no variety at all - it just means to keep your target audience constantly in mind.