[lusr]

Lots of good comments above, but here's a concrete example.

It can be a lot faster and accurate searching the source code for an answer than googling it. My most recent example: the .NET WebClient throws an exception ("ProtocolError") if it receives an HTTP 304 ("Not Modified") response. This makes no sense, but is it a bug? Did I use the client correctly? Or is it by design - i.e. a vexing exception (http://blogs.msdn.com/b/ericlippert/archive/2008/09/10/vexin...).

If you google for the answer you get a bunch of other confused people and a bunch of different advice, none of which is appealing. If you look at the source code you can quickly answer the question: yes, they really did design things in this brain dead way, and now my caching layer - which is supposed to be fast - is going to have to handle an exception every single cache hit. (When you're issuing over a million requests per day and you're paying for CPU time by the hour this design decision actually has a cost since exception handling is slow.)