There is a project I've worked on of late. It's a new CMS and I have to say that there is a rather significant and fatal flaw in its design – it requires all developers to work in the same data set.
Now this is by no means the only time I've seen something like this. I would be lying if I didn't admit that this has pretty standard fair for the industry, but then so was Subversion, and we all know how terribly that turned out. I will say that this is the most egregious example (as the underlying data architecture does not support even a cursory form of export) and the last time I encountered it I was also able to mitigate it by creating a truncated version of the data locally.