When a post gets six spam flags, it is deleted. However, the user account remains in the system.
When this happens, an automatic flag should be raised to allow moderators to check the account to see if it needs to be destroyed, similar to the PostVandalismDeletionsAuto flag.
I will periodically run searches, such as http://drupal.stackexchange.com/search?tab=newest&q=is%3aquestion%20deleted%3a1, and see blatant spam that has been deleted, but the spammer's account remains.
When combined with the feature that will allow moderators to annotate account deletion/deconstructions, SE will be able to get better information on the spammers.