Just a quick query for the other plugin developers out there. I'm trying to make my advertising management plugin as accessible as possible and was wondering how old a version of WordPress should I try and support? Are the majority of sites onto WordPress 3 and up? How many people are still using 2.9, 2.8? Does it make sense to go back to 2.6 is anyone using that anymore?
Also any suggestions on how to test for compatibility with what ever version you are support. I found quite a few old links for a plugin compatibility checker from Brave New Code, but it doesn't appear to be there anymore. I haven't been able to find anything equivalent. Am I really going to have to setup a server for each version and either manually or some convoluted test script try and install new versions on each to test?
Finally does anyone know of a comprehensive function matrix? Something that tells me what functions, filters, actions, options are available in each version.
The reason I ask is I recently added a few calls to get_site_url() to my plugin and got a ton of complaints that it broke the install process as it throws a fatal error on activation. All from users on WordPress installs older than 3.0. I've since switched to site_url(), but would like to avoid breaking things in the future.