Photo Booth freezes for >30s whenever I open it I've had this problem ever since I upgraded from Mavericks. Whenever I open Photo Booth, the application seems to be stuck on startup and I have to wait for like 50 seconds for it to become useable. A few months ago, it used to be like 20 seconds but it seems like the waiting time gets higher all the time.

Im using a Macbook Pro Retina 15 inch Early 2013.
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.