These cards automatically switch between 10 and 100 Mbs based upon what the rest of the network can handle. Also, if everyone except a couple of power users are satisfied with the 10BaseT system, the power users can be migrated to 100BaseTX hubs, along with the corporate servers. Suppose there are a couple of hundred users making the network too big. You can change from hubs to switches. Hubs share their total bandwidth among all concurrent users.
Switches allows several messages to proceed to their destinations simultaneously at full bit rate.
This cuts the bandwidth bottleneck way down. If you are not a large company you will probably not need gigabit LANS in the immediate future. That means that the basic technology you need for your future LAN already exists and is getting cheaper by the day. What you do today is use Fast Ethernet hubs with selective placement of switches in the network to eliminate bottlenecks. Show me the application.