Infographics are really nice to get an overview of a potentially big and/or complicated set of data. Here's a really nice (and easy to understand) infographic by Claudio Ferreira Filho about Debian's release timeline and number of developers vs. number of packages:

Overview of debian releases and development

Click on the image to see it full-size. Here's Claudio's original post

An interesting point is that was introduced apparently with the release of etch, so around 2007. Alioth is a server running the "FusionForge" software, which manages different development projects around debian like packaging and software specific to the Debian GNU/Linux OS.

Also, the small computers besides each release names indicate which architectures were added to or removed from support by the OS. So for example, in Etch, support for amd64 (most 64bit computers out there) was added and m68k (old Macintosh comps) was dropped.

Edit: gah, seems like the wordpress site was deleted along with the image. Talk about destroying knowledge! Book burner..