I've had this issue seemingly forever, with previous versions of Lightroom all the way to the current 5.7.1.
This hasn't changed with operating systems either, from XP through 7 to 8.1, or any other physical set up. My computer has also had different motherboards, processors, memory, and hard drives (currently i7 3770, 32GB, SSD raid 0), but the problem remains.
It's not always the same process, but mostly during cropping/rotating/spot removing when Lightroom hangs. Checking Task Manager shows it is running the CPU at around the 50% mark.
Is there any idea as to what causes it and if a fix is likely before they're carving my epitaph (probably to say "He was terminally sick of waiting for Adobe to fix the problem")?