Tools like time machine and vmware snapshots can make viruses less disastrous than before. You can rollback instead of re-imaging or worrying about removing all the malware.
Only if you're aware that the virus is running, and it doesn't do something disastrous in the meantime (eg, sniff your keystrokes while you enter a bank account number or log into the hospital records system).
That is good and all, but does little when the badware steals your passwords to your online bank.