When companies say your uplink or port speed is 100mb/s, do they mean you're sharing it with hundreds of other servers or you have 100mb/s that is for you? If its shared, than why even write 100mb/s because you will never truly achieve that. Confusing..
As a "rule of thumb", if it doesn't say "dedicated", than it is normally shared. The question would be, shared between how many servers?
Generally providers would normally have between 15 - 19 servers sharing a 100Mbps uplink, however as quantumphysics mentioned, you can normally get good speed on average as the provider will not cluster multiple high usage servers on the same shared uplinks to prevent bottlenecking.
I think people are confusing port speeds with the speed of the server to the switch or router; which is often 100mbit ; as from there you go on a shared network of your datacenter; this could be a 100mbit line but could be far more as that as well.
Our experience is that there is a huge difference between a 10mbit or 100mbit; while often the 100mbit is not reached; you have to wonder where the bottleneck is; and if this is even in the datacenter.
Some already complain that their SSH transfer doesnt get high speeds; while the issue has more to do with the protocol implementation as with the speeds of the network.