The link below suggests there is a feature on 6500's to detect unicast flooding & syslog when it occurs:
http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_note09186a00801d0808.shtml#detect
I have various 6500's running code much higher than 12.1(14)E but none of them seem to have this feature. Has anyone used this feature or know if its been abandoned? I'm sure I read somewhere there was a problem with this on sup720/msfc but cannot find any refernece to this.