I am seeing the same issue that many other people are reporting with slow shutdowns, logging off or switching users.
I am also having a problem with Registry Mechanic that may be related to the slowdown issue since both the shutdown/logoff/switch user processes and Registry Mechanic are accessing the registry.
When ZoneAlarm is enabled, Registry Mechanic starts fine and can perform registry scans but the program hangs when exiting (I do not have registry monitoring enabled, just manual scans).
Just like with the shutdown issue, it will eventually shutdown but takes several minutes to do so.
An interesting note is CCleaner does not have the same problem so the developers may want to look at the difference between how Registry Mechanic and CCleaner access/lock the registry as part of their troubleshooting process.
The shutdown issue also occurs when setting the display welcome screen setting with screen savers.
guess this makes sense since the issue is probably at least partly tied to the login/logoff process.
Just thought this might be some helpful information to use for troubleshooting.
I have already started a ticket with support.

Operating System:Windows XP Home Edition
Software Version:8.0
Product Name:ZoneAlarm Internet Security Suite