Typically I wipe and lube the chain every few weeks and clean the chain about once every 2-3 months. I wash the frame whenever it's getting dirty enough to bother me, but it is a commuter so I don't try to keep it looking pristine. Other than that, I pretty much just fix it when it shows signs of wear or problems.

I pay more attention to components wearing out than I do things being dirty... e.g. chain wear, worn brake pads etc. It's cheaper to fix these things before they completely wear out and/or fail, rather than wait for it to happen and damage something else.