Reshared post from +Ryan MacLean
Make Lightroom Faster!
Simple Lightroom 4 hack that allows you to remove modules from the binary, making things faster.
If, like me, you're still having LR4 speed issues – try this out. I can't say it completely resolved the issues I was having, but overall the app does seem a bit snappier!
NB: on a Mac, you'll need to right-click the Lightroom 4.app file and show package contents in order to start trashing things from within the "plugins" folder. I'd recommend making a backup copy in case you ever want to use the map, book and web modules that you'll no doubt remove.