Jailbroken, but not with any tweaks that modify it's appearance. I use it to add features that have been disabled by Apple or AT&T or whoever. I also really hate the bright blue color at night, so I use f.lux to make it more eyeball-friendly after hours.
The phone is pretty good stock, but the idea that someone else decides what I can or cannot do with my phone doesn't sit well with me on principal. It's my phone, and I'll use it the way that I want to, simple as that.
No lags, no resprings, no battery life hits - in fact, I'll wager that I get better battery performance than any stock phone, with better actual performance, too. And FaceTime has ALWAYS worked over 3G for me...