Now that my task system works, I can safely overhaul my set of debug and function return macros. Instead of using three or four they can be put them into a few more compressed ones. Since I want to have extensive logging functionality and possibly failsafe execution for all possible functions, I'm hardly using macro-less C code anymore. It's pretty comfortable as I don't need to manually add any debug message, return commands and so on. I'm speaking about a bachelor project right now, so anything to make it better is a plus and should be kept in mind. Also, it makes development and bugfixing faster since you don't add any tracing, external debugger or so - everything your need right there with a few macros!
So yeah, that's the way to go for the next few steps. I only have to pack my demos and binaries for my intership application this weekend, so I can fix up ITK with these macros to make the whole stuff looks less patchworked (seriously, it doesn't look appreciatable right now).