Flashback is the exception that proves the rule. As much as I like to disagree with people who suggest that the OS X is "fundamentally more secure than windows" (it really, really isn't) - it does tend to have many fewer active exploits than Windows Platforms do - and your average OS X system is much less likely to be loaded up with malware than your average Windows XP system.

Perhaps, but I find it unlikely that professional companies would let their workstations - Windows or OSX - get loaded with malware. In fact, I hardly encounter exploits or malware on PCs nowadays, and never at all in the few corporate environments I've been in.

No, Apple hasn't approached an AV vendor to help harden OSX. That was marketing FUD by Kaspersky that was later retracted. Kaspersky is conducting its own internal audit of OSX, and Apple has said that it would naturally be open to listening to any reports of vulnerabilities that Kaspersky might discover. This is far different than what was reported by computing.co.uk.