The real reason for which i stopped using them is that it doesn't work well with git. As soon as you've got more than one people in the team, it's over.
It is actually a solvable problem if you're willing to dig into the details of the file changes. It isn't pleasant, but welcome to life. Team members can make conflicting changes as long as someone is willing to dig through the mud to make them all agree with each other. I've been doing it personally for a long time, it isn't my favorite part of the job but it does enable significant parallel productivity.
