Scrum seems perfect if you approximate your developers as frictionless balls in a vacuum, but in the teams I've been in there are several problems I think that

Scrum seems perfect if you approximate your developers as frictionless balls in a vacuum, but in the teams I've been in there are several problems I think that Scrum actually decreased productivity. The developers build in lots of "fat" to their estimates: A story that could take 4 hours gets divided into 4 tasks that are estimated as 2 hours each just to be sure. I've also seen tasks that should take five minutes (eg. change the IP address in a config file) get estimated as an hour. The developers estimate very conservatively and the PMs and Scrum master aren't technically adept enough to do anything about it. Management seemed to like Scrum regardless because it provided transparency. I think they prefer the loss of productivity to a situation where they have no real idea over how their projects are progressing.