I'm not sure when this came out, but Google now has source code search. These guys never stop amazing me.
So what you need to do now is create a new bookmark in firefox. Point it to: http://www.google.com/codesearch?hl=en&q=+lang:php+%s
Give it a name and in the keyword field, put something like 'phpcode'. Save it.
Now in your address bar, type 'phpcode array_merge' and return.
IMHO, the worst part of Drupal is having to learn the API. The core developers are constantly refactoring the heart of Drupal, which is a good thing overall. But it makes it very difficult for the average developer to keep up with the API. Major version releases prior to 4.7 required a developer to make relatively few changes to his module to make it compatible with the new release. 4.7, on the other hand, requires pretty much a complete rewrite of a given 4.6 module.
The first revision control system I ever used was called RCS. It was the pre-cursor to CVS and stored all revision data locally. It was nifty but very limited and not suited for group development. CVS was the first shared revisioning system I used. It was rock solid, IMHO. But it had a few big problems, like the inability to rename or move files. Everything had to be deleted and re-added.
Since those days, I've used several other revisioning systems: Perforce, Bitkeeper, Clearcase, Subversion and GIT.
I recently worked on a project which required a updated version of the jQuery library. While there is the jQuery Update module, it only allows you to upgrade Drupal 6 to jQuery 1.3. If you really know what you're doing and want to upgrade beyond that version, you can either hack core or create your own simple module to do it. While hacking core is certainly the easier approach (simply overwriting misc/jquery.js with a newer version), it is very bad practice.
I'm not sure how it happened, but today I noticed that Drupal's menus were behaving very oddly. After upgrading to Drupal 6 and installing several additional modules, I noticed duplicate menu entries as well as other disturbing oddities. Items I was placing into the menu were not showing up. Menu items that I moved around were apparently saved but they did not appear properly in a dropdown context.