Photo Booth freezes for >30s whenever I open it
Do you have Dropbox? I found that if I quit the Dropbox app, most of these 'hangs' go away. Starting Chrome and Safari, Launching Mail.app all improved when I quit Dropbox. I still have Dropbox, and I restart it to get it to sync every so often, but I leave it off.

I have seen others with similar experience, but I don't use photobooth, so can not tell you if Dropbox is the cause. 

Also, I found a noticeable improvement across the board from starting with a clean install of Yosemite. My 13" 2011 MacBook Pro was nearly unusable following an upgrade to Yosemite.