Experiences with dynamically typed languages on large projects

Please post them. I'm an average programmer that needs static typing and a helping hand from the compiler and I know that there are tons of others too. From my minimal experience with python on last project (what else but for data crunching ), I felt that these languages demand quite a bit of discipline from developers. I have a feeling that it might work in a small team in a cubicle. But beyond that I'm a little skeptical. Please post your thoughts.

Ruby is the rival