Still have troubles with zoning into an instance? Check out the post below for updates!
The limit on active instances was originally implemented as an interim solution to ensure that all active instances perform smoothly. Within the last few weeks, we have configured and optimized our infrastructure to better handle the instance load, and many players are no longer experiencing issues with instance creation. However, to incorporate these upgrades across every realm is not a minor undertaking; it requires fairly complex coordination with third party affiliates who actually host the hardware we utilize.
This reconfiguration is already complete on more than 40% of the North American realms,the optimized realms are listed below, and the situation has noticeably improved on these realms. We are continuing to work towards the implementation of this reconfiguration for all realms, which we expect will resolve the instance creation issue for all players. We expect the optimization for all realms to be fully completed within the coming weeks, and would like to assure everyone that every effort is being made to ensure that this is completed as soon as possible.
http://forums.worldofwarcraft.com/thread.html?topicId=19377447673&sid=1