Princes Street will be closed to buses from 3rd September 2011. The closure will be in place till June 2012. The main difference to previous closures is that The Mound will also be closed to buses. This means that services like the 23 and 27 will be going via Waverley Bridge and St Andrews Square.
You can download a map showing all the temporary stops in George Street showing which services stop where here (single A4 sheet - pdf file):
Princes Street Bus Diversions Map