After installing OS X 10.8 Mountain Lion, a few things in our web development environment stopped working (namely Apache with multiple vhosts, BIND/wildcard DNS, Phusion Passenger and the rmagick2 gem, and postfix).
Mac OS X Quick Look is a great tool for being able to take a quick glance at a file's contents, without the delays associated with launching a full app. However, there are some limitations in the file types it's able to preview. As a web development company that deals with SQL on a daily basis, we were finally annoyed with the inability to quickly preview .sql files to the point that we decided to do a little digging.
Whenever I begin work on a new web development project, I seem to always have trouble remembering how to make a directory writable by Apache in Mac OS without giving full rwx permissions to everyone.