I'd be interested to see if it was possible to track and measure the inter-vlan traffic on a router or switch and flag a warning status when the device was hitting its limits. For example a cisco 2811 roughly max's out at around 80% CPU or 56-61mbps of inter-vlan traffic. It would be great to watch/monitor this in a table or something so we can see when a device starts to bottleneck.
Cisco Equipment Performance (per pps and Mbps) Cisco Forum FAQ | DSLReports, ISP Information
http://www.cisco.com/web/partners/downloads/765/tools/quickreference/routerperformance.pdf
http://www.cisco.com/web/partners/downloads/765/tools/quickreference/switchperformance.pdf