It is one license per machine... so you can't install it on multiple systems (home, work, wife's... etc.). The difference is you get support from Microsoft and can have multiple installs with no issues.
On an OEM you can't transfer the liscense to new motherboard on a new socket, which you can on the Full version.
It is easier to reinstall with in the first three months if you have issues. OEM verison is a little harder to do reinstalls (more hoops to go through... Im my experience.