One of the things DSLR manufacturer specs and online/magazine reviews commonly list is shutter durability figures. Prosumer DSLRs (e.g. the D700) typically list 150,000 exposures and pro DSLRs (e.g. D3) go up to 300,000 exposures. What does this number actually mean? Is this the actual expected working life of the shutter before it needs to be serviced or replaced? This is not a very large number of exposures, especially for a DSLR, where taking pictures is essentially free. I'm not a pro, but I often take 1000 pictures a week--does this mean that if I buy a D700, I can expect its shutter to go belly up every 15 weeks?