There's a nice post on the 37 Signals blog on the distressing -- and damaging -- perception that you must work punishing hours if you work for a startup. I haven't worked for a startup in several years, but you can't follow tech culture without seeing this ideology on a daily basis.
I've never been a long-hours guy, though I work today in an org where the always-in-the-office people are celebrated and people look at me a little funny when I mention that I usually go home before 5:30. Personally, I've never seen much of a benefit to working impossible hours. In college, when I tried to pull all-nighters, I realized that I was essentially useless after midnight; I was so tired, and my mind became so clumsy and slow, that I would have been better going to bed and hitting the books fresh the next morning. Since then I've never had a job that I couldn't excel in within the confines of 40 hours per week.
Could I have done a little better if I had forgotten about my wife and my life and lived in the office? Maybe I could have found another 10% or so at the bottom of the barrel, but the cost would have been very high, and sooner or later I would have burned out and quit. On the other side of the coin, the people I've known who work evenings and weekends also call in sick a lot more often than I do, they disappear for long lunches, and some of them take cigarette breaks that last for hours. When I'm here, I'm here.
Overtime is overrated. It's too easy to show your commitment by staying late or coming in on Saturdays. You don't need to be talented to work long hours, you just need to be willing. The more significant achievement is to do excellent work during business hours, go home at the end of the day, and come back the next day ready to go.