Once in a while! At a previous job I had asked for a weekend off and didn't get it. The head boss was a cow but my supervisor was really nice. On the Friday she asked if I thought I was coming down with a cold (hint hint) Sure enough the next morning I wasn't feeling well
my first summer job i called in twice, i think. i HATED that job and the pay was awful so i really didn't feel bad about it. the job i had the next couple of summers my boss was really cool and pretty much let me take a day off whenever. i tried not to take advantage of his flexibility, but considering the number of times he and 3 other guys from the office would take off early to play a round of golf i probably wouldn't have been missed.
I didn't call in sick though, I would make something up like having to meet a potential Landlord or something - then I didn't have to stay away from work!