I just read this entry from one of the planet freedesktop bloggers.
It reminds me of an email sent around my place of work with a title something like "Can anyone tell me what this function does?". It came from real source code in our system at the time and contained a function at least a few hundred lines long. The very first line of the function was an unconditional "return 0;". Just as the author had, most readers spent a few minutes delving through the complex control flow of the function before looking at the code in in a linear fashion and seeing that first "the function does nothing" line.
Dead code could very well be the worst sin in software. I you want to keep past code around for future reference, use a revision control system. Don't clutter up the current codebase with historical oddities, especially when they appear at first to still be used.