The IT staff at my former employer saved copies of all email that went through the server... indefinitely. No, they didn't tell employees they were doing it. And yes, they had a search engine so they could do across the board searches of whatever terms seemed interesting at the time.
I find it interesting that different companies are going to different extremes. Some are limiting their exposure by trying to delete all mail and others are saving all mail in order to be able to comply with court orders (or perhaps just get a bit big brother-ish.
For a REALLY strange twist, the company I'm speaking of forced employees to maintain mailboxes under 100MB... while the server admins never deleted a single email that hit the server.