uh
the industry marker for toner usage is usally 10% coverage... which mimicks a printout of a page full of text. of coures pictures use much more toner.
also, toner is a solid, so it settles unevenly. the usual taking out the cartridge, and rocking it to redistribute the toner is called for towards the end. this can extend usefulness by a dozens of pages...
toner lifetime depends on the size of the machine, and amount of toner in each cartridge.
be warned that some companies tout their usage based on economy mode, which is by no means what ppl do with papers. economy mode uses much less toner, so they use those numbers. for the HP printers, if you print text, economy mode generally prints the outline of each letter dark, while the fill of each letter is very light (not much toner).
for my 6Lse, a smaller laser printer, HP says its 2500 on economy mode. this is not one of those HUGE machines with the large cartridges, so it is much lower than what large corporate offices use.