At my airline (a large regional in the US), our rules are as follows. "Contract" denotes they're a limit based on our union's contract, "FAA" denotes they're a legal limit.
Duty Time (start to finish of work)
Max scheduled: 14hrs (contract)
Max: 15 1/2hrs (contract)
Max: 16hrs (FAA)
Flight time in a duty period
Max scheduled: 8hrs (FAA)
Max: Unlimited (as long as we stay in duty time limits)
Legs in a duty period:
Max scheduled: Unlimited
Max I've ever done: 7
We usually (80% of the time or so) change planes every time we return to the hub.
We're required 1 day (contract) / 24 hours (FAA) off in every 7 day period. We can't fly more than 30 hours in a 7 day period, 100 hours in a calendar month, or 1000 hours in a calendar year (all FAA limits). But, remember, for every 1 hour of flight time, we often are at work for 2-3 hours.
At my airline, we're staffed such that we have approximately 4 crews per airplane. We're horribly understaffed and have to cancel flights constantly due to lack of pilots. When november and december roll around, I have no idea how we're going to have pilots to fly our flights... we're all flying so much to make up for our staffing shortage that we're all going to hit our 1000 hour mark for the year sometime in november. So, enjoy the busy winter holiday travel season... you can expect a lot of cancellations due to no crews. But, thats getting off on a tangent...