What's wrong with modules? I think it's a lot more comfortable when i have all the source in front of me, instead of linking to dll's containing i don't know what, but has probably a lot of bugs. And if something drains performance, it's probably because someone made a function too userfriendly and errorhandling.

When working in teams it's probably also best to have all the source available for all members, but it should be also well documented and all changes made to other's code shoud be commented.