I once coded std::vector and more why ? Bad education mostly, turn out that stuff is rather good :) Took me the hard way to find that out. I still need to replace all that code.
What I mostly learned: pick ONE thing, and assume you will spend 10 year to complete it as life will keep interrupting.
Also if you ever decide to code an audio engine again, could use some help :p (from a person like you) (find me on freenode.org)
I rewrote std::vector so I could separate arrays of objects that have constructors/destructors and objects that don't. These are almost always used by other data structures, not by themselves. I still use std::vector when I just need a dynamic array that respects constructors and proper copy semantics. The problem I encountered was that std::vector refuses to integrate nicely with other data structures.
While I'm sure many would still cry foul just because they can and don't understand what I'm doing, I can assure you that my re-implementation of std::vector is purposeful and used in specific circumstances, not as a generalized replacement, which is the real issue.