BTW, my understanding of dual speed 10/100 hubs, they actually provide an internal 2 port bridge between the 10 and 100 segments.
For routine traffic, normally you wouldn't care. However, if you wanted to use such a hub to perform traffic analysis, it's possible the bridge might not forward unicast traffic if it knows receiving MAC isn't on other bandwidth segment.
If there's a bridge, it might also be possible to extend hubs beyond normal Ethernet repeater restrictions (i.e. the 5-4-3 rules for 10 Mbps, and 2 Class II hubs for 100 Mbps) if you forced traffic across different bandwidth segments.
