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