[_delirium]

AGPL isn't exceptionally common, but it's used in a reasonable number of SaaS type niches, where the other common license is "don't release source at all". For example, Launchpad and Gitorious are AGPL, while their main competitor, Github, is closed-source.

Ghostscript is probably the most widely used piece of AGPL software. That one's driven mostly by their dual-licensing strategy (they want proprietary SaaS providers to buy the commercial version of Ghostscript).