I agree that a blog is not a good place to put code (or documentation, for that matter), but calling it a waste of time in general is over-generalized.
A blog is a very good tool for letting others know what you're working on, and if there's a big public interest in the things you do, then it's really worth the time. The alternatives are mailing lists (to which usually most people who would read your blog aren't subscribed), and answering questions directly - which is much more time consuming, and reaches even less people.
The point is of course that you should only blog if you actually have something to say, and which is of interest to at least some part of the Perl community.
I for one love to read more from the testing/qa people, and from the Perl 6 and Parrot folks (naturally, because my main interest is in the same area).