Our largest clients (both large banks over here) are still on XP+IE8 on their standard desktops. At least we are no refusing to support anything older (there are still pockets of IE7 at RBS it would seem) but I'd love to refuse to support IE8 too...
There will not be a massive XP infection on April 8th, it will come at least a few weeks after that ;)
We are charging extra for any custom work to allow for testing and bug resolution specific to ancient combinations, and refusing to address superficial issues at all without a full change request and appropriate payment, but we simply can't refuse to aupport XP+IE8 without telling them to take their £20,000/month elsewhere.
We do have big new potential customers on the horizon, and they are more up-to-date in that respect. Maybe if these people don't upgrade soon and we do get huge new contracts, we'll be in a position to say "your choice, upgrade or go be a problem to our competitors" come the next contract round. I hope so.