Well, writing this from the sandpit, I took my boots and socks off to work it out. By the time I finish my current tour (late 2009), since ops started in Iraq in 2003 I will have spent approximately 16 months sitting in the desert in Iraq or Afghanistan on ops.
You can add to that all the various exercises ranging from a week to a month over the same period and being on call for a significant amount of time when I wasn't on ops or exercise. And I reckon I'm probably one of the luckier ones!