Do you use windows, cygwin, and git, and does gitk annoy you like crazy when you try to copy and paste commit hashes?
The solution is pretty simple: each time you need to copy a new hash to the clipboard, copy something from a different field in gitk first. Any old text will do.
For a full explanation see my original post on the Softwire blog.
Alternatively, check out sourcetree, which could replace git gui and gitk altogether.