Travish,

the switch doesn't have two ipadresses in his arp-table, it just updated the macadress with the ipadress from the victim to the attacker's ip adress, so you will cut off the vitcim in this example.
Now if you'd try a Man in the middle attack ( in this example sit between the switch and the victim ), with lets say ettercap, you'd poison in two directions, thus in the arptable of the switch you'd see the victim's ip adress with the attackers macadress, and the other way around on the victims arptable. In this example the victim would still be able to communicate and surf, while you read what he's doing with for.ex. tcpdump or another sniffer.

Anyway try ettercap for the mitm-attack, and this to see the difference :

Code:
 #!/bin/bash

counter=0

while [ "$counter" != 1000 ]; do
 sleep 1
  nemesis arp -S <victim-ip> -D <switch-ip> -m <attacker-mac> -r
done
This is a very simple script to temporary poison a switch, but which would create a victim cut-off. the -r is crucial cause it tells its an arp-reply.
If you tcpdump then on your attackerbox, you'd see all present connections originally to the victim's box contimuing on the attackerbox.