The registry is a transaction-based database. Its performance is nearly independent of the size of the database. A large registry won't "slow Windows to a crawl" due to its size - that's just a fanboi myth.
What may slow it down is if the user being stupid and thinking that it's OK to remove applications by deleting filesystem directories. It's not, and it may cause problems (including slowdowns because you haven't actually removed the application).
If you don't uninstall programs using the "Control Panel" -> "Programs and Features" tool, you're a bad admin. You will mess your system up.
Here's another perspective on the registry:
http://en.wikipedia.org/wiki/Windows_Registry#Advantages_and_Disadvantages
I don't understand all the hate for the registry - it's an alternative approach with advantages and disadvantages.
(For me, the remote registry editing is a big advantage. If a system is stuck and you can't log in, it's usually possible to remotely edit the registry and fix it. With .ini (pref) files, you'd need to mount the disk on another system to edit the files.)