Earlier this week I was in a meeting were someone stated that it was better to write your own IOC container than just using an existing one (the most excellent Castle Windsor in this case). I was just baffled to hear such statements.
The argument for writing your own container was simplicity and the learning curve for new developers on the team. I strongly disagree.
I can't think of anything simpler than downloading an existing IOC container that has a near flat-line learning curve, like the Castle Windsor container. About a year ago, I introduced it into the team. No learning problems whatsoever. Just read two blog posts about it and you are on your way
But the main reason I disagree is that I strongly believe that we have to provide business value instead of writing yet-another-IOC-container. We have to solve the problems of our customers. They simply don't care about IOC containers.
Scott Hanselman has a nice list of Dependency Injection Containers. Pick, choose and get over it!