I use 1/2-liter amber PET screw-top bottles exclusively and love them. I got a deal on 6 cases of Mr. Beer PET bottles at BevMo for half-price, plus my 10% member discount about a year ago and have never had a single problem in 25 batches or so. I just bottled one yesterday, as a matter of fact.
Pros: They're lightweight, virtually unbreakable, fast and easy to cap, and the caps are reusable. You can also tell when your beer is carbonated. They're cheap compared to swing-tops.
Cons: You can't sanitize them in the dishwasher. Probably not good for long-term storage due to potential oxygen permeability. They don't look as classy as a glass bottle. You have to pay for them.
Overall I have no plans to go to glass, though I have bottled some mead in Grolsch bottles. I wouldn't use them for beer since they're green.