CodeJunkie, I agree with k-ww. The majority of manufacturers of ICs supply a recommended circuit either in the datasheet or application notes, which will tell you the type and value used for capacitors. These values do not necessarily tie in with the theory (and in many cases you won't get enough information to calculate it).
For example, the datasheet for the LM7805 linear regulator converting 9V to 5V says to use 0.33uF for input, and 0.1uF for output. Although the notes in the datasheet also implies that the output capacitor is not absolutely necessary for it to work, it'll just work better with it there.
From a practical point of view, you probably don't want to have to buy every single capacitance value that a datasheet might suggest you use, so knowing a bit of theory would let you make an educated guess as to whether it's ok to use the nearest higher or nearest lower value as a substitute.
My advice to you is to learn the theory if you can, but don't get too hung-up about it (unless you're doing precise oscillators, or filters, or power circuits), and go with the datasheet recommended values