Indexes
 

I've noticed that very few people use them in their database tables. Do you use them (besides primary key)? Why or why not?

For those of you who don't know:
An index is basically a secondary storage area for your table. It associates the value of the field indexed with the row in the table. Thereby making your searches far faster (when you have large databases), although your inserts are slower and the space taken up is greater.