A couple things to check. First, check to be sure that the destination mac address is in the cam table. If not, we are going to flood the packet.
Also, please make sure that you have all your end user stations set with portfast enabled. Without it enabled, these ports can generate TCNs, which cause the cam table to go into fast aging (15 secs, vs. 300secs). Check the following document for more details and troubleshooting steps.
http://www.cisco.com/warp/customer/473/17.html
Dave