People that engage in churning are a bit self-conscious (source: recovering churner). Simple fact is you don't churn if you don't have to- it's not worth your time.
> Another layman question, what does this do to your credit score?
Opening new credit cards lowers your credit score- it adds weight to the single debt category(mortgage has a house backing it, a credit card doesn't), lowers the average age of credit lines (someone that has paid a home loan on time for the past 20 years is more 'reliable' than the naive 18-year old college student das company is preying upon), and, if you open too many at once, gives the impression you're desperate, insolvent.
Another layman question, what does this do to your credit score?