Howard M. Lewis Ship: Synergy allows me to use my desktop keyboard and mouse on both systems. The mouse travels off the left side of my desktop screen onto the right side of my laptop screen. Focus follows mouse, at least in terms of system-to-system, so I can type on one system (say, the desktop), move the cursor over to the laptop, and type into the active window there (without clicking).
In order to get a compatible version on Ubuntu, I followed Phil Crosby's instructions (Google cache):
sudo apt-get install libxtst-dev ./configure -x-includes /usr/includes -x-libraries /usr/lib --prefix=/usr make sudo make install
Being able to copy and paste from Windows/XP to Ubuntu rocks!