Which is sad because I like to have all kinds of users but it's really really difficult to accommodate for all you guys browsing on a mac.
Please hit me with hints to make life easier for myself if you have some...
I'll put in the time to boot into a Windows partition and double-check IE9, but when it comes to OS X/Safari, I've got little recourse but to crossing my fingers and bank on Safari's Webkit rendering being the same as (or close enough to) Chrome in Windows and Chromium in Linux.
Safari DOES have a Windows version, but I've never seen it enter into the conversation at all. Is it guaranteed to have true rendering/display parity with the OS X variant?
Might want to try the Windows version of Safari then. The JS engines in Chrome and Safari have some quirks between them and can behave differently in some scenarios, mostly things that JSLint would catch though.
The only thing you'd need a Mac for really is ensuring that your colors/contrast look good, and that fonts are readable (on account of the font hinting).
The other option, of course, is to either buy a Mac, or build a Hackintosh.
Microsoft allows you to run Windows in a virtual machine, Apple bans you from doing so. That's why I develop on a Mac; Apple forces me to.