From a security standpoint, I've seen some major downsides to managed services unfortunately. So many moving parts and the problem with each managed service is that I've noticed many users of them do not become as well-trained as they should... So you end up seeing developers using 5-15 managed services and having only a cursory knowledge of the security implications behind them... Coupled with the fact that many managed services backseat security documentation and training, and it can be a nasty recipe.
I definitely see the benefits as well though - It's nice not having to deal with the upkeep and maintenance and being able to do a few click launch,