Study the two kerned samples to the left. The difference is subtle. I prefer the letter spacing of the lower sample but kerning is a personal judgment call. Most computer fonts today are proportionally spaced, meaning they are pre-kerned. Custom kerning is very labor intensive and it is usually reserved for use on large display type.
Courier is the infamous non-proportional type carried over to PC's from the typewriter.
Unfortunately, it still has a critical flaw. It discounts the font's kerning pair information. This cripples the power of PhotoText. Extensis is working to correct the problem in future upgrades. The PhotoText example given at the beginning of this Text section still gives a strong idea for how text might be handled in future Photoshop upgrades.