Count us among the sites noting reports of Google Toolbar’s bad behavior with 404 error pages. As the old saying goes, it’s not a bug, it’s a feature.

Google’s Matt Cutts explained why everyone should calm down and take a breath. The Toolbar behavior had been disclosed in a couple of places, but probably didn’t receive enough attention.

“If you

Astute webmasters quickly realized the value in making their 404 Page Not Found messages offer more than an oblique error message. A custom 404 can help a visitor get back on track within a website; the custom 404 proves its value quickly by serving as a retention aid.

The Seoker blog witnessed something disturbing after adding the beta of the Google Toolbar to a computer:

Google grabs the 404 error code returned to the web browser in certain situations and instead of displaying the 404 error page of the website you are on, it creates a custom 404 error page – made by Google. The “new” 404 error page ‘conveniently’ includes a Google search box and if used by a visitor will drive the visitor away from your website.

“I find it humorous that Google, who has horrible 404 pages, is replacing 404 pages for other sites with the toolbar,” said Rustybrick at SEORountable. “Besides for the humor and irony in this, replacing a 404 page with something else is purely evil in many webmaster’s minds.”