Nothing's cooler than writing a bad-ass site or application and watching it gain popularity and a significant user base. By the same token, nothing's more frustrating that watching your app fall on its face when its running under high load. [...] Before you say, "throw more / better hardware at that mo-fo", why not take a moment and learn about APC: Alternative PHP Cache...

He describes the caching software - what it is and how it can help you and your application - and includes examples using a CacheManger class to store and set values quickly and easily.

• don't see the need and/or benefits of a good programming IDE like Zend Studio or Eclipse PDT
• have never used some form of version control like Subclipse
• don't use a consistent methodology
• don't use test-driven development
• don't return content but echo or print it from your functions or classes
• return HTML, not data, strings, or objects.
• don't allow intelligent error handling
• you think reusable software equals/requires your code to be OOP

Now granted, some of them are a bit more high level than others, but if you're not headed towards a lot of these, you might change paths, hop out of that comfort zone and branch out into the community and the language a little bit more.

There's some good advice in there, and I thought it'd be a good idea to quickly add a bit more detail about the separate approaches that Mike raises.

He goes over the APC caching, memcache, the "gzip trick", the "Not Modified" header and optimized SQL statements.

He also mentions one thing that Mike didn't mention - a split between static files (no PHP needed) and their dynamic cousins. Having a more pure Apache (no PHP installed) can help give a minute jump in speed that, depending on the size of the site, could really add up from a user's perspective.

So we've got potentially slower code, and we can no longer just open up our simple PHP script and follow its execution from the top of the file to the bottom. How do we figure out exactly what's going on inside?

He doesn't go through the installation of XDebug, but he does give an example (complete with screenshots) of how to use it in conjunction with two other applications - WinCacheGrind for Windows users and KCachegrind - to work with the output XDebug produces.