First of all keep in mind that your host does act as a moderator in a Shared/Virtual environment because a server only has so much in the way of resources. Those resources (RAM, Processor time, storage space) have to be shared between all of the clients.
Depending upon the host, when a client outgrows his allocated resources they could either look to increase the resource allocations with a larger plan or depending on the load size that the customer has grown to, begin discussions on a dedicated server.
Bottom line is get to a larger account or your own dedicated server as quickly as possible because if it is throttled down you will not have anyway of determining how much potential business you are losing or missing.
Hope that helps!
