Scripts heavily dependent on a dll.. I've seen quite a few myself. aIRC rings a bell. Too many supporting functions become entirely processed via the DLL to the point the developers only write event hooks for the DLLs, minimal mScript. An awesome way in my opinion if done right.

But hardly a reason to disfavor DLLs -- if an update to Windows or mIRC breaks a dll, it's just as likely an update/change in mIRC would break more scripts than a single DLL.