Oh dear, now I feel guilty because I don't feel guilty.
I've got to figure the proof is in the pudding. My daughter is happy, well behaved and fun to be around. I may not do everything right (lord knows that's true), but I must be doing _something_ right.
I do feel badly when I've lost my cool (and there have been a couple of instances that I'm still kicking myself for). And while it's never good to lose your temper, kids are resilient and as long as you're not abusive (I'm not), yelling once in a while probably won't scar her for life.
Of course, I wonder if someday she will have forgotten that she was a happy kid and turn into a sullen teenager who thinks her parents are idiots. But my job isn't to be popular, it's to create a person who will be a contributing member of society. Keeping my eyes on the goal of creating a functioning adult helps me. When in doubt I ask myself "What kind of adult will she be if I do (or don't do) this?" and "How does this further my personal values?"