blimey, i hardly ever change the strings of my guitar (once ive experimented and found the perfect set anyway).
For instance, my main gig guitar used to be a Squier Jagmaster II. At a gig last Xmas i cut my finger during the first song and covered the whole guitar in blood - i wiped the guitar off, but you can still see bits of red on the strings. in fact i reckon the blood improved the tone (blame the SD Invader installed in the bridge - worst pickup EVER!).
I just like the smoothness of worn-in strings.
My main gigging guitar now (Yamaha RGX321-FP) is a metal guitar and so has a flloyd rose trem. Needless to say ive nenver been brave enough to even attempt to change the strings - even though it really needs some heavier ones (it came strung with 8's...faaar too light!)