At my previous gig, I was a technical lead in a pretty large technical project. Because the company didn't want to budget for having software testers in our main office in New York (and, more or less, rightfully so; most of the company's internal software was coming from Manila by that point) and deadlines were tight, I had to be online with our testers over there for most of their shift so we could resolve bugs somewhat quickly. While I came in much later than normal to adjust for this (12pm instead of 9-10am), I was also working later as a result (b/w 2am and 3am, usually).
Being pulled apart by two other similarly-major projects didn't help either and my team-mate was way too busy and burnt out to take on much more. My sleeping cycles were definitely thrown out of whack for a while, which never helps. As a result, I was more irritable and less tolerable and social than I normally am. I usually enjoy spending my free time going out with old friends and making new ones, which became practically impossible with this setup. I thought I was fine since my health was still fit and it didn't feel that bad, but I realised how bad things actually got after I switched jobs a few weeks later.
It's not about the hours you work. It's about the results that come out of your time at work. Someone that works three hours a day but produces significant value for his or her company is way more useful than someone who puts in his or her "eight hours" with nothing to show for it.