If your looking to move your current exchange system to the cloud i.e (office 365) and others. The first thing you will find out is that it will not take away the number of in house servers you have. In fact in our case we had to add a few more server then we are getting to take out. If you already run ADFS you are good to go but if not you are looking at 4 new servers aleast. There are other configs the add to the number of servers you need or lessen the number, but you will have to find what works for you. This should not stop anybody from looking into moving Exchange in the cloud. I think the benefits are well worth the start up cost, but it's always good to know what your getting into before hand.