I have heard that the maximum block size means that the Bitcoin network has a maximum throughput. What is this maximum?
From the Scalability on the wiki page
Today the Bitcoin network is restricted to a sustained rate of 7 tps by some artificial limits. These were put in place to stop people from ballooning the size of the block chain before the network and community was ready for it. Once those limits are lifted, the maximum transaction rate will go up significantly.
There's also some charts comparing to other payment networks