In preparing a new Java Posse episode to go out, I read this on Jeff Atwood's Coding Horror blog. It moved me to make a posting since I see this so often.
"#30: Developer gold-plating. Developers are fascinated by new technology and are sometimes anxious to try out new features of their language or environment or to create their own implementation of a slick feature they saw in another product--whether or not it's required in their product. The effort required to design, implement, test, document, and support features that are not required lengthens the schedule."
If you don't know the person/persons on the project upon which you are working that are doing this, then it might be you! In addition, I would just say that the place to do stuff like this is on your own open source project, not on something with a deadline and clients waiting. It's not wrong to want to try something new, but if you believe it enough to really do it, consider doing it on your own dime.