Manually adjusting the ragged edge of text on the web seems like silly advice to me. In print, sure, it makes sense because you have absolute control over everything. But with variable screen sizes, fonts and display devices used for viewing web content, I don't see the point in manually tuning text spacing when the chances are good others will see different spacing.
A lot of (product) websites routinely use fixed size div containers for the markup. So if you know your audience, it is really quite simple to manually justify the text for the target browser/OS combinations. This clearly doesn't apply to expansive blog posts, news sites, forums and such, but the improvement of the visual appearance of the smaller blocks of text is very much worth the effort.
You can specify the exact size of the div, but you won't know for certain the font being used. Yes, if you know your audience well you can get it right for a lot of them, but I think that misses one of the strengths of the web. Instead of spending your time optimizing for a particular configuration, optimize for a design and layout that looks good in many configurations.
