As I've mentioned before, the problem of a single database file is that it can easily get corrupted and with KeePass, every password in the file is accessible to everybody, so nothing for groups. It does have lock files, but I wouldn't completely trust them to lock a database against incoherent changes.
You might want to check out PassPack:
Passpack lets you store personal, work and client logins in one master list, then choose what to share with whom and when.
All updates are automatically synchronized.
You may change settings, share passwords and set permissions in bulk or on a single record; one user at a time or with entire user groups.
There is a free version, but the Pro and Group versions are relatively cheap at $1.50 or $4 a month, respectively. [No, I'm not affiliated with them, it's just a solution to your problem ;)]
This would also effectively hinder people to just "copy the DB on a stick".