I read your posting and I looked for more info on Cisco.com, I found a document with indepth arp information and commands. I would think thst if the mac-address arp table was full and unable to forward any additional layer 2 frames, then the new entry would not be established and entered into the table, until an existing entry timed out. There is a command you can use to setup a loggin alert when the arp table reaches a certain limit. HTH

http://www.cisco.com/en/US/docs/ios/ipaddr/command/reference/iad_arp.html