My primary home machine is a Linux deskop, and my primary work machine is an OSX laptop. I do most of my work on the Linux box, ssh-ed into the OS X machine -- I recognize that's the reverse of usual setups, but I love the awesome window manager and the copy-on-select X Window selection scheme.
My frustration is in having separate copy and paste buffers across the two systems. If I select something in a work email, I often want to paste it into the Linux machine. Similarly if I copy an error from a Linux console I need to paste it into a work email.