Patch 3.3 obviously is having its share of bugs, some more severe than others. People are reporting inability to zone into instances, often times met either with the dreaded "Additional instances cannot be launched" error or just flat out lagging out so long that they're ported back to Dalaran or wherever the system decides to drop them, entirely unable to enter the instance.
Some of the issues have been addressed, some haven't.
Blizzard has released the first part of the list of known issues with patch 3.3. It will be expanding in the future, so don't get too upset when you don't see a bug on it. Remember that it typically takes a couple days for a patch to get all its kinks worked out. Just hang tight, enjoy some some lore and trailer action, and things will be fixed before you know it.
The full list of known issues after the break.