Larry Osterman offers some words of wisdom regarding the differnce between a developer understanding cryptography (as in "which algorithm should I use" and "what are the tradeoffs?") versus a developer implementing a new cryptographic algorithm. Most developers can learn the basics, but it takes very special skills (Larry's description and I agree) to design something new that is really secure.
The bottom line: if you know a little about cryptography and feel confident you can create the next best algorithm, think again! Learn it but use the best proven methods in your development work rather than dreaming of your own.