Will changing the server date/time cause problems?

[Justin Pasher <justinp(at)newmediagateway(dot)com>]

A client of ours has requested that we change the time on the server to 
match their time zone (one hour ahead of us). Are there any know issues 
or gotchas to look out for when bumping the server time forward an hour? 
I couldn't imagine any issues occurring, since it's really just like the 
server when 1 hour without performing any activity. Obviously any fields 
in the database stored with a time without a timezone would be off 
afterwards, but that's not a huge concern.

Another client has requested the same thing, but their time is two hours 
behind us. This is the change that I'm more worried about, since you are 
going to have some data/time overlap on the server after the change is 
made. Are there any known issues with this situation in Postgres? Should 
everything be shutdown prior to the change, then restarted again?

Thanks.

Justin Pasher