Ok, I admit it.
I suck at applying body filler.
To be honest this is something that just didn't occur to me suddenly--I've known this for years. And when I was first beginning to work on cars this caused a greater set of problems then it does for me now because I have more experience dealing with my lack of skill.
Now I know that filler isn't a magical substance--that it is only created to cover minor imperfections. So I spent the better part of a day on Saturday with a hammer and dolly (and a small grinding wheel on my dremel tool) carefully going over the areas that I patched on the left front fender to make sure that the thickness of filler required would be minimal.
Starting with a specialty filler that works well over welded seams, I skim-coated over all of my repairs, then sanded this down smooth, lightly tapping down any high spots that showed up during my sanding. Then I switched to a standard lightweight body filler for the rest of work.
Why no pictures? Because I'm a little embarrassed by the quality (or lack thereof) of my work. A good body person will apply a thin, almost perfectly smooth coat of filler that requires only a modicum of sanding. Not me. I leave ridges and low areas and, in general apply too much filler. So it looks like crap--at least until I sand it down.
When I do sand it down, I'm using the longest sanding blocks I have; the goal is to eliminate any "waves" in the finish. I nearly sand off all of the coat before adding another, slowly building up miniscule layers to achieve that smooth finish. Again, the professionals would likely be able to do this in a single pass--but for me, a little elbow grease serves to remind me just how skilled a craftsmen a good body person is.
I'll post pics once it gets into primer. Well, maybe.