Quick clarification point to prevent confusion:
Currently there doesn't seem to be much to worry about - business as usual for most customer.
There are two items of interest, though, discussed in the Windows 7 Application Quality Cookbook and the What's New in Message Queuing 5.0 TechNet article :
Note - Windows 2000 leaves extended support on July 13th, 2010, ten years after it was released, as documented on the Microsoft Product Lifecycle website.
The "What's New" article also mentions "Ability to Handle a Large Number of Queues" but that's just an optimisation rather than new functionality. There will have been a number of other changes to improve performance - this one was just more noteworthy than the rest.