I got my Prius, the everything-but-the-kitchen-sink version, in late October 2003. It now has 50K miles on it and has been absolutely flawless; the only time it's been in the shop is for routine service every 5K miles, and for the rare-but-proactive service bulletins that are inevitable with a car this technologically sophisticated. Again, I've never had so much as a hiccup in the three years of ownership, and Toyota clearly takes pride in its build quality. I drive a lot of urban freeways and surface streets with lots of stops, and have averaged 47mpg over the life of the car (with a semi-lead foot). There is no doubt in my mind the next car I get will be another Prius.
The smooth acceleration; "space pod" exterior; roomy interior - the fold-down rear seats have cleared enough cargo for chaise lounges, 8' long boards, and more that you'd swear couldn't possibly fit. The climate control and Smart Entry systems are outstanding features. Nav system and Bluetooth phone
I wish the 2004 had MP3 playback capability from CDs, but Toyota has added that (standard) to the '06 and later models. That's pretty much the only thing I can think of to make this a perfect vehicle.