I've watched many try to use Act and other contact managers in a shared environment. While my experience is with prior versions I'll warn you to get your refund policy in writing if they have not solved the old issues. We watched this and others crash the database requiring restore from backups and for every user to logout and back in. Unless you build this on top of some sturdy SQL (like MySQL) and rock solid server I'll say you may get to repeat history.

Bob