Everything costs half, including research. But unit support still costs the same.
In my opinion the most noticable difference is the importance of forest. The 10 shields that cutting it down produces all of a sudden make a huge difference on the build. For example: a seafaring civ can create a harbor in a remote (therefore completely corrupt) city in just 5 turns just by cutting down a forest.
The other difference is (if I remember well) that worker actions still take the same time. So you need more workers to keep up with infrastructure in relation to your population.