What happens when mac's get a virus?

Well, first and foremost their users freak out, and don't know how to handle it. They've bought into the myth that "macs don't get viruses". Which is outright wrong, as the case may be.

Although a bit like closing the barn door when the animals are gone, there's free antivirus for mac that you should install. http://www.sophos.com/en-us/products/free-tools/sophos-antivirus-for-mac-home-edition.aspx

Apple has stated that it is going to release some software to kill MacDefender, ("In the coming days, Apple will deliver a Mac OS X software update that will automatically find and remove Mac Defender malware and its known variants."), but whether it'll kill whatever software's troubling you is unknown. You might, after all, have some UNknown variant of Mac Defender.

Some removal steps are listed here: http://support.apple.com/kb/ht4650

2

Poisoned JavaScript is delivered to the browser, (none are immune), and this powerful language then manipulates a computer and installs these "rogue" items.
Since Mac's are now on the bad guys radar, adopting good security strategies (adopted from years of malware infestations in tens of millions of PC users) must now be employed by Mac's: and that means concentrating efforts on PREVENTION, not removal.

Firefox, with "NoScript" controls what automatically deploys from the browser, and is the #1 defense against several vectors of malware.
https://addons.mozilla.org/en-US/firefox/collections/dunbar-pappy/dunbarpappy/

Also, the default configuration for Safari has "Open "safe" files after downloading" checked (by default). This setting is under "Preferences" in Safari and is at the bottom of the "General" tab (the first tab).
It must now be disabled (unchecked) at all times.
And, do not rely on "signature" based antivirus. Criminals update their rubbish daily (just like the good guys) and change names and other aspects (like a fingerprint) in order to get around detection.
Prevention: not removal.

Can Linux be far behind???? Stay tuned.

Don't know, there haven't been any viruses on OS X yet.

Some people have managed to infect themselves with trojans. Removing those trojans is very easy.

Apple will be releasing a patch shortly for that virus. Check their website.