Why isn't my Drupal block cache working

A quick gotcha explanation if you find that Drupal's block cache isn't working.

Chances are this could be described somewhere, but after a bit of Googling and it not turning up, I figure put it up!

Pretty simple really, Drupal won't cache blocks for User 1 (block.module, line 28):

* Note that user 1 is excluded from block caching.


There you have it!