I've been using PHP for a bit over a year and half. It's come to my conclusion, that I've never used MySQL in any of my applications. I think I'm scared of reliance.
I tend to use either a simple flat file (like WorkSimple) or pjjTextBase (Torrentino for example) because they're quite easy to manipulate. I'm not sure why I don't use MySQL, being PHP's soul. Everything you see nowadays for PHP uses MySQL.
None of my applications use MySQL (or anything that is 'modern'). Hell, Sysode, Torrentino and Ticketo (my larger projects) all use PTB. Plus, flat file is faster. Skip the middleman, and write directly to the file system. Additionally, I tend to keep my projects/scripts small.