Here's my opinion, and it's just an opinion. I choose not to support anything older than IE8 for my personal projects, but I am a student and not officially working in the field yet. I do also include the following footer:
This website makes extensive use of new web based technologies and coding.
We recomend that you make sure you are running the latest version of your current web browser.
Obviously in a career scenario, whatever a paying client wants should be considered providing the price is right for the extra time involved. If you answer to a boss, I suppose you wouldn't have a choice on the matter (besides arguing your point).
IE9 thankfully supports a lot of new features, and as such I think it is definitely fair to bring IE9 on board as a browser you should attempt to cater for.
Ultimately though with any project, you should ask yourself if a particular element is really needed and relevant to the project. There's nothing worse than people just slapping on drop shadows and rounded edges for no apparent design reason than "because they can".