Originally Posted by Lombard

As I and others have already stated, it all depends on how much shifting you do. There is no "magic mileage". I am happy for you that you haven't had any problems with STI shifters eating cables............yet. Which generation of shifters do you have?

And as I have mentioned, if you haven't replaced your housings in some time, it's probably a good idea to at least unwrap your bar tape and check for corrosion - especially if you sweat a lot. This is not something you want to find out about while you're riding - much worse than having a shifter cable break.