If you have congestion in your network that causes your users to complain, QOS might be the answer. It really depends on the specific applications in use, as well as your network. Sometimes more bandwidth is the right answer. If you have real time traffic like voice or video you definitely need QOS.
What problems are you having?
tcp or udp...damn, im not really sure on that...we are using analog cameras into a digital encoder to display the video via ip...that encoder is connected to a 3750 switch then to a 6509 switch where the mgmt vlan is configured...im still reading up on QoS, do you have to put the QoS configs on every switch it will hit for access of video?
Is it always jittery, or only when network traffic load is high? With your all LAN topology I would suspect packet loss as your primary problem. Do you see any interface errors on the 3750 encoder interface or 6509 interface connecting to your video display? Is it possible to test by connecting the video display to the 3750, or even directly to the output of the encoder to be sure it is a network issue?