On the Working Software blog there's a recent post looking at correcting a mistake that the developer made when choosing the logging method of his application - pushing the output of print_r into a file.
recently deployed a job on which the timeline was so tight that my ability to type quickly was what made the difference between delivering on time or not. Everything was rushed, the budget was tight, it was one of those real seat of the pants deals and there was far too little testing done. [...] The only problem is that, in the 5 minutes before the site was supposed to go live, I didn't really have much time to thoughtfully prepare a logging system to record all this stuff and, in my haste, I settled for [a file_put_contents of the print_r of $_GET and $_POST].
Obviously, this solution is useful for casual browsing of the information, but if you need any real data from it, it's a real chore. To help you with the task, they've put together a snippet of code that can work through your print_r output and return it in a much more handy line-by-line result. Full code is copy-and-paste ready in the post.