Almost never. I play mostly the same thing though. Sometimes, the fills will be completely different because of how I'm feeling. If I'm tired, I play some lazy-ass fills. For instance, last weekend, my band, The Bon Scotts played 7 sets in two days. By the 7th set (at the third venue of the weekend I should add), I was pretty much just holding on. Not to mention I was cranky/hangry as well. Sometimes, you're just not as in to the gig as you know you should be.
As far as reading goes, I have developed a basic roadmap kind of system that works for me while I figure out new tunes, and that works for the pop stuff I'm doing. Especially since the band is adamant about no charts on stage. When I was in college, I played a fair amount of big band stuff, and also played with a 10 piece funk band that leaned more towards the acid jazz/fusion vein. That band was intense, no charts would've been suicide.
It all depends on the gig I guess. You should definitely know how to read though. I'm not saying you should get to the point where you're one of those freaks that can play pepper spilled on manuscript, but get comfy enough that you can make it through a tune without anyone noticing the bits that you missed, and then make sure you catch them the next time through (if there is a next time that is...)