We're debating displaying twice as many ads to IE6 users as we do to everyone else. For our pay web services, we're debating including an IE6 surcharge.
While we'd love to drop IE6 completely, it feels crazy to do so while it's still 20% of visits. But there is definitely a lot of extra development time needed to keep things working for older browsers.
In both cases, we'd make it 100% clear why they saw more ads and paid more, with instructions on how to upgrade.
If everyone did such a thing, maybe we'd see the financial/annoyance incentive lead them in the right direction to browsers that don't cost as much to support.
It's been a long week, so this may be a bit crazy, but I thought I'd get some discussion going as Friday comes to a close.
Either way, you'll probably want to run this by a bunch of actual customers. People with the sort of personality quirks that draw them to (and make them good at) programming might respond to this very differently than customers/clients at large. Also, note that some people will not be allowed to change web browsers, e.g. for administrative reasons. (Whether or not they're good reasons is beyond your control.)
I don't know if it's a good idea from a business standpoint, but I like it.