I had once a network with 10bT hub on it. I proposed to the customer to install a 100bT switch to speed things up.
at the time I did not know the importance of good cables.
the network was slower after the hub-> switch exchange ! lots of errors, collisions, so on.
only 2-3 computers were ok, the ones that had good cables.
the other had badly paired rj45 plugs (not the right pair at the right place of the connector)
I rewired the bad cables and everything went back to what they should be.
There's your problem-- hub. You can't get collisions if you use a proper switch or router that directs packets where they belong.

All Ethernet modes are "unusually robust": 10Mb is slow as molasses; 100Mb is fast, but not terribly critical of moderate mismatch (one jumper is fine, but as wraper said, ten in a row might not work out so well), and 1Gb measures the line and compensates for its frequency response, to an extent. If nothing else, an exceedingly poor line will fall back to a lower, less susceptible mode, maintaining a connection, if not a fast one (which is still good enough for, say, connecting to your average cable/DSL modem*).
*Well, U.S. average.

Tim