IDEs - This can be tricky but I have gone through a few different progressions over the years. Sometimes being on a project or a specific feature can trigger an upgrade. For example, someone implemented a feature using LINQ so what was an ASP.Net 2.0 project became a 3.5 project overnight. Other times, it is just what is currently in use. A point here is that a change can impact a whole team so it isn't a change to be made lightly.
Bug tracking tools - This is also in that land of centralized stuff that has to be carefully managed. Since this is a QA tool, I'd hope they have their own policies of how often to look for updates and when to install them as sometimes new features can be cool to get. The dev team equivalent would be when to update the wiki.
Version control - These are individually managed since most of us use Tortoise SVN so we each have a local client copy. So, the updates are done when someone wants to do it. I like to stay up to date as much as possible, personally.
OS - While part of this can be controlled on a department basis, there are enough different pieces to update that sometimes I'll run an update on my own. I'm not sure when we'll move to Windows 7 as I know we aren't going to Vista and I'd think at some point we'd get off XP as I've been on XP now for about 5 years as before that I was on Windows 2000 Professional for a few years and NT 4.0 before that.
PC - There is a policy that every 3 years we get new machines I believe. When I started where I am now, I was on a P4 box, so the upgrade to a dual-core box was very nice as well as a good RAM boost from 2 GB to 4 GB.