On one of my tanks, 3-4bps with a 5lb cylinder w/ reactor, about 5 months. It sounds so far like the experiences of the OP, proaudio, Wasserpest, and myself are on par with each other, while Daximus' is outside the norm - he's getting a lot more out of his cylinder than I would expect given its size.
To clarify, though, when talking about length of time the cylinder lasts, the important stats are cylinder size, *bubble counter type* (the generic glass bc's have much smaller bubbles than a JBJ, while the cylindrical plastic ones tend to have larger bubbles), bps, hours per day, and possibly regulator pressure. I say "possibly" because, while it's clear that gas at a higher pressure takes up less space than gas at a lower pressure, it's not terribly clear how much pressure is acting on the gas in a bc past the needle valve, especially given varying back pressures due to methods of diffusion.
Anyway, I would guess that what you're looking for is cylinder size and JBJ-style bps, as well as hours per day. That should give you a basic framework to compare.