Managing large volumes of content, handling large numbers of visits. We are familiar with and have successfully managed issues that arise from large volumes of content, especially text, images, and audio. The content management system for B92.net, the principal news website in Serbia, is used by 500.000-plus users per day (2+ million page views) with close to no downtime for about 7+ years now. B92.fm, a podcasting portal, uses a database of 200.000-plus audio files, from 2hr- length podcasts to usual singles.
Optimization. Proper understanding of inner workings of MySQL allows us to significantly improve a troubled application’s performance, and we have been known to make the already-failed projects alive again. Same applies to PHP/Apache optimizations, although the gains tend to be less spectacular (as there is less room to do wrong in the first place).