I enabled it on all the items we get from a couple of vendors.
It did not work well for us because of the difference in the logic that MRP uses vs the reorder report.
 
Most of our ordering occurs as a result of an item hitting the reorder level.
 
My only complaint with MRP is that it suggests a buy when the available qty <= reorder level,
and the reorder report suggests a buy when the available qty < reorder level.
 
We have set our reorder levels based on the logic of the reorder report.  Because of that,
MRP suggests purchases that we do not want to make (when available qty = reorder level).
 
For some people, this does not make a difference because they set their reorder levels (safety stock in MRP speak)
based on the MRP logic.  However, for us, it is a big problem.
 
I haven't thought it out completely, but if MRP was changed to match the reorder report logic, It may still work
fine for the current MRP people.
 
I would love to use MRP so that we can avoid hand entering POs.