The lack of good email clients on Linux is a real shame. I'd love to have something like Sparrow or Mailbox. 1password is also a sad thing to be missing.

As for the others, we have locate(1) for searching and rdiff-backup instead of Time Machine.

As for having desktops like that, if you mean monitors, then there's a great solution: Synergy. Hook up monitors to both computers and use Synergy to connect them.