Penguin:
I left UPS two months ago. Trust me: you made the right move! I was a supervisor, and had been with brown for almost seven years. I never took a sick day, always worked hard, treated my union people fairly....never even got a single "thank you." Last year, I started looking for a new job after our manager started to slowly put the screws to us. He wouldn't let us take our discretionary days, and kept moving our vacations, and when we complained to HR, he said we needed to plan "around peak and planning periods" (which, ironically, is ALL THE TIME), and HR agreed with him. He wouldn't let me leave "early" after an eleven-hour day to go to my sister's confirmation. He let two of our admin positions go through attrition but guess what: their work never went away.
So I got a new job with a new Fortune 500 company. Sure, it's a little less money salary-wise, but on an hourly scale, I'm making more here. The new company has an incentive program like the MIP, but instead of working to meet "fuzzy" corporate goals, half of my incentive is based SOLELY ON MY OWN PERFORMANCE. I also negotiated for my vacation time, plus I get sick and personal days that I can bank for the rest of my career. Mostly though, the new job has much less stress, and I have yet to be screamed at for a mistake.
You made the right choice. Don't even look back.