I use mine pretty steadily, all day long...I still get a couple of weeks out of them generally.....after a couple of weeks though, I find that if you pull them apart the wicking material resembles a thick coffee.....nasty.....even then, after rinsing them in cheap vodka, I use them as drip tubes for a week or so before I finally toss them.....handy for finishing off those bottles of eliquid you tried but don't use often enough to commit a cartomizer to.....
if you really want to get your money's worth, I heard of a technique to re-pack them.....a small straw big enough to fit over the wick....wrap tea bag material tightly around the straw....insert that in a larger straw that will fit inside the cartomizer so the tea bag material is squeezed between the two straws.....slide it in the cartomizer.....wiggle both straws free, leaving the tea bag material inside the cartomizer.....reuse.....