Usually, if I see a client using IE, I’ll talk to them about it when we do the site launch.
I’d highly recommend trying to catch it sooner. I actively engage this issue, and talk about browser support (specifically, what it means, not simply which browsers I will support) before I even give an estimate.
My initial conversation goes something like …
I understand where you’re coming from, but I can really see that conversation backfiring. IE users might have a lower “browser ed level,” but that doesn’t mean they think that anything could possibly be better.
The truth is IE is a bad choice for a browser.
Older versions, yes. 9 is so-so. 10 is very good (not that I like it, but it is very good). A better approach to the conversation would be “you should upgrade.” For those on IE8 -who cannot upgrade- it becomes a discussion about how this is ten years old, and simply cannot do what modern browsers can. In this case, I would actively suggest switching browsers.