I had the crotch darned a few years ago. They did a good job, but they didn't cover as big an area as I had expected. The darn is holding up, but the denim just outside of it is pretty much see-through. I wear them occasionally, but I always feel like I'm one large step away from it giving out completely.
And thanks. Those were my first Japanese pair. They took a long time to get that way...I only wore them in the summer, and my office didn't allow jeans until about a year ago.