I've touched on the topic of field schedules in the past, but Silver Fox's recent post reminded me of one of my problems with a common "odd" (i.e. not 5 on, 2 off) schedule.
The standard non 5-and-2 schedule I've worked is a ten-four. That is, work 10 days and have a four day weekend. The problem is trying to preserve those four weekend days. It's awful easy for the schedule to slip and for the project manager to suggest that you give up a day or two. After all, it's mid-week for everyone else.
The last time I worked a 10-4, I had to travel to the hotel the night before (stretching the shift to 11 days), then I was persuaded to work "just one more day to finish up" (ok, now it's 12 days), and then I got the stink eye when I ran into an upper management type and she found out that I was "taking a day off" for the final day.
So if you work a 10-4, or any other oddball schedule that has you working through a weekend and gives you additional time off during the traditional weekday, be wary. And avoid returning to the office during normal office hours if you can help it.