Irregular publishing frequency is the seventh mistake in the top 10 blog usability mistakes by Jakob Nielsen (2005). It is generally a good idea in all web publishing (blogs, webcomics, etc) to give your audience some vague idea when they can expect your next masterpiece. If users come back again and again time after time only to find that nothing new has been added, your faithful readers can soon become ex-readers. So have some kind of regular publishing frequency and stick to it. Or if you want to publish longer and more insightful articles with plenty of time between them, you might want to encourage your readers to subscribe to your RSS and/or Atom feeds, because feed subscriptions effectively negate the impact of readers dropping because of irregular publishing frequency.
If you know you will be publishing in irregular intervals, let your readers know that so they don't expect regular service. And if you know that for one reason or another you will not be posting for a while and the blog will start collecting dust, post "on hiatus until" message telling no new posts are to be expected until certain time. Keeping a regular publishing frequency is not easy, so it is good idea to keep some draft posts ready in case deadline approaches and you get the dreaded "writers block" (unless you want to write about that). Bottom line is, let your readers know when they can expect your next magnus opus and don't give promises of publishing frequency that you won't be able to keep.