Drupal core hacks - thinking about it?

Funny results from searching Google for ‘drupal core hack’:

Do not hack core | drupal.org
29 Jan 2009 … “Do not hack core!” This phrase is commonly heard in the Drupal community. There are even t-shirts made with this phrase and this cannot be …
drupal.org/node/144376 - 16k - Cached - Similar pages

Documentation: Info on Core Hack [...]

Drupal performance tuning (2) and a patch to the memcache module

Two methods are explained below to serve some of your (anonymous) pages entirely from memcache. The second one is nicer and follows the Drupal way of handling things. The first one is more like a hack.
The hack: modify index.php
If you’re allready using the Drupal memcache module, there is a somewhat clunky way to get your [...]

Drupal performance tuning

This won’t be the last post about Drupal performance tuning I guess.
Some steps you can follow to increase the performance of your Drupal-based website (if you need so), in no particular order:
Don’t let the database handle the cache

Add memcache support (no surprise there): Install memcached on your server (or on a few of them). On [...]