Form validation with PHP. Help!
After hunting round on the web and browsing my own library of methods, I realised that I didn't know quite as much about this as I thought. After several hours beating myself up (metaphorically speaking), I remembered this PHP User System Form Validation video tutorial from Think Vitamin. It's an excellent tutorial that provides a useful starting point for validating forms with PHP.
Anyway, the tutorial helped me recode my particular form. Great work from the presenter Jim Hoskins and the Think Vitamin guys and gals!
Update August 2012: The link above is no longer there and there's no replacement AFAIK