In this post from Business Logs, Mike Rundle points something very clear: Either support Safari, or lose customers. He's sooo clear that makes me feel like wearing shades.
There is more than one example of website which does not work with safari; some days ago I pointed GAP as an example of shop banning Safari users, some months ago I found myself unable to buy a ticket in easyjet because they redesigned the site and now you can't select a date with safari - which is absolutely stupid... I would accept to not to have some super propietary aesthetic filter which just works on IE, but ... not having a working date dropdown box? that's plainly an idiot's idea.
And, as somebody says in the comments for that blog, the mac users base is increasing and I don't think that the growth it's going to stop in a near future.
So, stop optimizing your site for IE.
Start thinking standard.