Raises an interesting point.
On all my home systems I use an adminstrative log on for maintenance but have normal (non-administrative) log ons for normal use. That way I can run a 'light' antimalware package like Microsoft Security Essentials. The performance overhead of the mainstream antimalware is crippling.
This only works if the logged on user cannot instal software or make system changes, malware uses the same privileges as the current log on. It is inconvenient, especailly when you have a new or fresh system, but still (IMHO) a worthwhile trade-off.
HTH

