Well now you know the benefit of leaving it in quarantine, a bit like sending a patient to intensive care rather than the morgue.
Another benefit is with the file in the chest, you can retrieve information on the file name and its original location.
If you look at the avastUI, Real-Time Shields, File System Shield, if you haven't rebooted (and unfortunately you have) there should be information on number of files scanned/infected, the last file scanned and last infected file - you can also click the Shield log link.
You can also check the raw report text file containing information on the file system shield and detections:
C:\Documents and Settings\All Users\Application Data\AVAST Software\Avast\report\FileSystemShield.txt winXP.
C:\ProgramData\AVAST Software\Avast\report\FileSystemShield.txt Vista, win7.