Here is what I like to do. I create a hole wizard hole (or series of holes) the diameter that I want the slot to be. Then I create an extrude cut use the slot sketch tool... centering on all of the hole wizard sketch points. I set the edge of the slot sketch tangent to the edge of the hole wizard hole. I can then create axes on two of the hole wizard points (optional). The axes can be used for mating at the next assembly. You can then mate hardware to the axis and use the hole wizard feature to pattern all of your hardware.
This works especially well when you want a clearance slot for a given fastener and don't want to "look up" the appropriate diameter... just use the appropriate hole wizard option.
-Dustin
Professional Engineer
Pretty good with SolidWorks