I spent 8 of the most valuable weeks of my life discovering that opera stage management was NOT for me, although I was (and continued to be) an accomplished theatre SM. I know it's been years since this thread was started, but I think it bears revisiting every so often, because until you have actually done both, you have NO idea how different an animal it is. It is vital to understand, as stage management folk tend to be a tad perfectionist and hard on themselves, that it is possible to be excellent at one and hopeless at the other. If you can do both, you're like a left-handed pitcher for the Yankees at the World Series, and you will work forever!
A couple of points that didn't get mentioned in the past thread that I'd like to hit:
1. In opera, any costume change to take less than 20 minutes is a quickchange, and requires paperwork, a dresser, and a backstage changing area.
2. In opera, a costume change is the removal and/or addition of ANY article of clothing, including a mask or a shawl.
3. In opera, you never know when someone will whisper, "here, hold this a second." If you take it, do not look back to see what it is. It could be anything from a retainer to a bear.
Yes, a bear. This is opera.