Scott - flash is one of those things that people either get totally, or they just use as a fix of some sorts without really delving deeper into it because it doesn't interest them.
I use flash for a massive amount of my work, tailoring the amount of flash use and the type of flash use to the magazine I'm shooting for.
Where I see it's biggest value is to improve the light you already have. I shoot throughout the year and there are two main times that flash, both on-camera and off-camera, is invaluable. The first is on those dull, dark days when I need some extra light, plain and simple. The second is in high summer when the sun is high and the light is terrible through the middle of the day, all shadows and highlights. Flash helps me controls the shadow.
If you're using just a pop-up flash then I can't really give you any pointers others than watch the flash power and what surfaces it hits and what surfaces it hits first (to avoid blown highlights). Diffusion is possible but it's not going to be as effective as diffusing a larger, more adaptable light source.
If you're thinking about buying a flashgun then you need to A) read up on using flash and how it affects both the exposure and how you think about the mechanics of a shot (ISO, shutter, aperture), and B) experiment to gain a good idea of what the flash can do and how you can then apply it to your photography.
Aside from the initial concept of aperture and shutter speed, using flash is probably the next most talked about subject for aspiring photographers because it's easy to see how a flash affects a photograph, but not so easy to understand how.
I suggest that you look at the strobist website and/or buy a book called 'Light: science & magic' - both are invaluable resources, especially strobist, which has a 101 section for people starting out.