It seems to me that when submissives talk about being a "service" sub they have these glamorous images of serving him coffee on their knees - blow jobs - hot maid outfits and never really getting dirty. (who would want to get a french's maid outfit dirty that probably cost more than a week's wages?!)
It seems to me that a lot of the images that come to mind when we think/ discuss D/s relationships - involve hot images of sexy activities.
Service involves making meals he wants to eat when you aren't hungry or don't really like what he wants for dinner. It means watching one more television show that you can't stand, It means washing his dirty clothes and folding them and putting them away so he doesn't have to think about it and probably won't even notice.
Service doesn't involve Masters standing with their hands on their hips watching your every move - with a whip dangling over their shoulder....threatening a good beating if you miss a fleck of dust. The reality - the truth - is you clean and cook and take care of him because deep down inside you have a burning need to do it.
And if at the end of the day - he finds a whip or flogger and you get your ass beat - or you have mind blowing orgasms - it probably has nothing to do with the service - but more with his needs.
So make sure - before you sign up for a "service subbie" position that you can see past the fantasy and into the reality - and do it for the internal pleasure it gives you to make His life easier.