I must say that I applaud Google’s policy:
“We support the current and previous major releases of Chrome, Firefox, Internet Explorer, and Safari on a rolling basis. Each time a new version is released, we begin supporting that version and stop supporting the third-oldest version.”
This makes so much sense to me and something that I have put forward in my office too. I think that we have stopped supporting IE6 but I would bet that elsewhere on the web (or especially intranets) that decrepit piece of software is hanging on by its fingernails. Sadly, this policy has been criticised by a Microsoft employee!