Just been given Lightroom 5 and installed it on my MacBook Pro. Did a few "learning" photo fixes and then went into iPhoto. iPhoto just hung up, spinning disc and the computer would not respond to anything. Did a hard shutdown holding down the ogg button until it responded. Tried iPhoto again, same result.
Rebooted and "trashed" Lightroom from the Applications folder, re booted and everything fine, iPhoto running as normal