I do my own E6, mostly because of cost. I shoot 4x5 transparencies, and developing lab costs are just too high.
DKT mentions above the need for absoute consistency, and he's right. Small changes in temp and times, if they are uncompensated (and compensating is more an art than a science, I use time and color dev pH) will give less than ideal images. But then, I'm an enzymologists, and copared to enzyme activity assays, E6 is quick and sloppy, so it's easy for me.
In the end, we do our own color development because we like doing it, not because it's easier or better than a lab.
I've done C41, and it's very easy. Since the color balance gets adjusted on the enlarger, temp isn't as exacting as E6. But printing RA4 is hard, as one step is just so dang short (45 sec developer!, it's awkward to do in a rotary processor.