I sometime find them interesting to look at but overall find the user experience very poor. It bugs me when scroll does not behave as expected. I also find that it slows the scrolling or jumps around too much because it is resource intensive. I prefer normal scrolling sites, no weird gimmicks.
I was pretty impressed by them at first and my portfolio site needs a new redesign so I got all excited thinking I wanted to do this type of site and even started a mock up for it. Once I got past the new excitement I think I started realizing it may not be worth it for the user experience and bugs like mentioned.
A majority of the ones I see now just come across as very distracting and unnecessary such as is [Webdesignerdepot’s](http://webdesignerdepot.com/ “http://webdesignerdepot.com/”) new redesign.