Email retention and archive files

We have Exchange 5.5 with a 30GB Information store. It was hard getting decent limits put on the server. A political mess at best. Now we have that in place the users are using PST files to store mail on the file servers. The files get corruptedeasily and constantly need to be restored. They take up a ton of space on the file server. I am curious what others are doing that are facing the same problems.