I flew a lot of hours in November, and I figure I racked up 39,007 miles. All domestic.
I estimate that I would average anywhere between 30,000 and 40,000 a month. When I used to do a transcontinental commute (2 or 3 times a month) it would push it up well over 45,000 (of course, I wasn't working on my commuter flights).
A typical 2-day trip for a flight attendant might me something like this - LAX-ORD-MCO, then MCO-DEN-LAX. 5157 miles, and you do it 6 or 7 times a month for a total of 30,942 or 36,099.
International flights don't necessarily mean a lot more miles....for example you would work the 3-day SEA-NRT-SEA trip 4 times a month - 38,152.