Very specifically line 24 in my SVN chechout contains the following number, but there is no explanation as to why this number is there; I can guess why it is there, but it shouldn't be my task to figure out why something is there. A comment above this constant should say why exactly it is that value and not some other value, why it is important for the system, etc.
uint256 hashGenesisBlock("0x000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f");
Lol
As the name of the variable indicates it, it's the genesis block. I guess it's the public key of the first ever bitcoins.
This is certainly not the best critic of Satoshi's code you can make.