At the date of this post, IE 8 has been out for 4 months and IE 7 for 2.5 years. Why am I still seeing threads about designing for IE 6?
The reality of it is that your average person knows little about what a browser is, and why it's important to keep your software up to date. Part of this reason is that nothing ever breaks when they are running outdated technology. Developers need to keep moving the web forward and stop supporting older browsers. A step in the right direction is telling your user when their browser is out of date. In our next update, users not using the latest major version of Chrome, IE, and Firefox will have a notice on their screen explaining that their browser is out of date with a provided link on how to upgrade.
By implementing features like this, you're saving yourself time and educating your visitors.
UPDATE: The day after I posted this Google announced they are discontinuing support for IE 6.