I have a couple of questions since this thread seems to be active again...

1) How many subsets of 737 pilots are there at CO? I know that pilots can fly most (if not all) versions of the 73 with a single type rating and differences training. I guess what I am curious about is how that translates for the airline/pilots themselves.
- Is there one "737" category that goes all the way from the -500 to the -900ER?
- Is there a "classic" group vs. a NG group?
-Within these groupings, is there true flexibility...i.e. could a pilot fly one leg on a 73G, the next leg on a 739ER, and then back to the 73G, and so forth?

and

2) What are (generally) the overnight rest requirements for domestic and Canada/Carib/Central Am/Northern S. Am flights?

Actually, to simplify matters, a better question would be: how long does an AIRCRAFT have to be scheduled RON in order for the same crew to be able to legally fly her in in the evening and out again the next morning, assuming only one airplane of the type on the ground and no staggering of crews between inbounds and outbounds? Is domestic different than international, even with generally the same aircraft types? CO does not do standing overnights, correct?

Thanks for any insight.