I have a number of sites that I have tracked for years using Google Analytics. Most currently show about 35% or 40% of visitors using a version of IE.
One shows only 5%. (Chrome and FF make up most of the traffic, according to GA). 75% of visits are from Windows. It's a public website with a broad, non-technical audience.
The site gets new traffic through many sources: organic search, and several ad campaigns using Facebook, StumbleUpon paid discovery, and Adwords, all targeting desktop computers, and we are getting a significant sample (some number of thousands of visits a day). Everything else looks completely normal.
The site is mostly HTML 5, with sufficient support for IE 7 and 8 to make it usable. Users might run into minor bumps when filling out forms and the like, but it mostly works. Plus, I am only looking at new visitors.
When I segment the traffic (e.g. just StumbleUpon, or just Facebook) I don't see significant differences -- still very low IE usage. I haven't checked the server logs yet (hoping to avoid that hell :-)
I am fully aware of GA's many limitations and shortfalls, but of the 20 or so sites I have access to on GA, none is showing this pattern.
What could possibly explain this huge discrepancy?