Other things to see and do
(partial list)
TCP bytes seems normal or low, TCP packets
normal or slightly higher, TCP flows high
look for SYN flood or similar strangeness
Ratio of TCP to UDP/ICMP (any) decreasing
packet loss on network causing TCP to back off
Watch high-traffic hosts and hosts which talk to
many other external machines
find the owned warez box faster
Look for traffic which shouldn't make it through
your firewall configuration