Sometimes. Other times I just use them as bases to create something completely different. And sometimes I just like doing photography just to make my desktop background pretty. ;D
1) Kill a sim. Make sure you have a spare sim so when you get called by the science facility to try and bring them back to life they can take your urn. The experiment will 'fail' but you will be left with a playable ghost. 2) Try for a baby with a ghost.