Ever since my update to yosemite, Lightroom has been acting up weirdly, it works all fine upto a random point where the busy wheel appears, from then on it becomes painfully slow. does not respond to changes i make, Brush tool and Spot Removal tool take time to show up. Undo takes 4-5 seconds even for the smallest change.
don't do lens corrections has worked for me. (stop laughing rob cole) I do lens correction before export/edit in pse and then I remove the l/c from the raw file. Yeah bit
Someone posted upgrading 5.7 fixed his problems. I'm still on 5.6
Hope that helps. There is big thread about this drama.