Especially when creating web sites intended for technical audiences, wouldn't it be best to end support for obsoleted browsers? Would this not provide additional incentives to upgrade?
Recently I (and my colleagues) had to decide whether it was worth our time to try and support anything before IE8, and in the end we decided to redirect any IE6/7 user-agent to a separately set up page explaining that the site is not accessible with Internet Explorer 6 or 7. For us this was easy once we saw from our analytics that under 5% of visitors to the site were using IE at all.
Have you had to make choices like this and, if so, what was your reasoning behind the decision?