Also,
If you let your support contract lapse, and you later want to have support, you will have to back pay all support, and possible migrate to whatever the current licensing is.
We are experiencing this now and it SUCKS!!!!
We had a concurrent Session license from 1998, and now have to migrate to the named user. It will cost us 3 - 4 timees what we originally paid due to the number of processors we use, and the minimums for Named User.