I try to keep I/O out of my modules unless that is the main function of the particular function or method. If I have to issue a warning, I use one of the carp functions.

If you want to do I/O, try to design it so the argument can deal with either a file or a filehandle (whether input or output). It's nice to be able to get the results back into a scalar sometime, but if you don't get that far, somebody can use IO::Scalar.

I think most people will have an answer that parallels their thought about die-ing inside a module. I've decided that it's one of those landmine questions where most people already know what they think and will force the users of their code to do it their way. Their way usually optimizes the process for their initial use of it, and everything else has to work around that. It's mildly annoying, but that's life.