I love working part-time. I've worked part-time since the birth of my first child, 18 years ago. I'm still a downshifter and too old for ER, now just earlier than it would have otherwise have been. Most recently I declared semi-retirement...I'm still working to improve my stache, : cutting my hours from .7 to .5 blew out my retirement date by 2-3 years. Since I cut back I'm enjoying life AND work much much more. 4 days weekends are just great. My improved quality of life has easily compensated for a couple more years in the workforce.
I think it might depend on your industry, and what happens when you work less hours - different jobs have different inherent structures and requirements....I think there might be an optimum number of hours for a particular job, that gives the best life-work balance. Its worth experimenting with. For example ,when I worked 0.7 I worked Mon, half day Tues, Wed and Friday. The half day, never was a half day because I was there and "stuff" happened. Thursday was spent mopping up the chaos at home from Mon-Wed and trying to do business hours errands. Then work again Fri, and just a regular weekend break. My workplace treated me like I was more or less working full-time. By dropping Friday, I now have a 4 day break every week, and its very clear I am only there part-time, and in fact they have employed an additional part-timer to cover. So my current arrangement is hugely better, disproportionately so compared to the pay cut.
But if as Marty says, you have the sort of job where you spend a lot of time unavoidably doing emails/calls etc on your day off, then its possibly not worth it. I have gone for a particular type of job description within my area, since it lends itself to part-time work. There are other interesting things I could do, but they need a full-timer. Part-timers do need to have a better ability to create and enforce work:life boundaries I think.