I don't know exactly how/when/why this behavior started, but recently whenever I perform a paste operation (mostly this happens in a browser, from one tab to another), my entire system (2013 MBP running Yosemite) will hang for a number of seconds (~30-60sec).
I'll copy some text from one page then paste it in another (e.g. a form, a gmail compose window, etc.) and on the paste operation, instead of the text getting pasted, the mouse cursor becomes the circular, colorful "waiting" icon. At this point the entire system appears to be "hanging", although I can move the cursor. For example, during the hang, even my Parallels Windows VM is unresponsive. When the system returns from the hang, the text is not pasted.
I also tested this with a non-browser application (Notes) and it still causes a hang, so that's why I'm implicating the OS.
This is obviously a fairly serious and limiting bug, so your help is appreciated.
edit 1: I tried disabling the auto-correct spelling setting (under Keyboard), but this doesn't appear to help.
edit 2: This appears to be caused by Parallels Desktop. I shut down my VM and closed Parallels Desktop and the issue goes away. After restarting the VM, the issue persists. Parallels has fairly tight OS integration, so this does not surprise me. I'll take this up with Parallels and report back if there is a solution.