Most of my work is video, so I have a fairly decent continuous lighting kit for that. In addition, when I took some "basic" camera classes after getting my DSLR, the lady who taught it preferred to shoot without flash, and stressed getting things right in the camera (less to do in post). And every flash image I have taken (using the on camera flash) just did not look good to me. Too washed out. Even most of the flash images I've seen from others just don't look good to me.
However, I have run into at least one situation where an off-camera flash would have been helpful... and I've seen some images here that to me are stunning and an off-camera flash was used. And I've seen some stuff where a good external flash was used as "fill" for daylight shots. So I'm jumping on the external flash next month, and I plan on spending a lot of time learning how to use it.