It depends on the situation. We just visited our parents out of state, and they had us pick up a bunch of liquor from Costco since it is so much cheaper there than a normal liquor store. So I bought them about $40 of vodka, they had told me they were going to pay me back.
They didn't. I also didn't ask. My parents paid for dinner for us twice, bought gas for his boat that we used the entire weekend (he didn't even go on it at all!), etc. When he heard about all of the stuff I was selling on eBay, he asked if everything was ok and to let him know if we need help. (We're fine--I'm just trying to get rid of shit that I don't need).
So, for $40 of liquor, and about 3-4 hours of work (2-3 of which I enjoyed) my wife and I got free lodging on a beachfront property, lots of love for our dogs, use of a boat, use of many toys, etc. Yeah, mom and dad said they'd pay us back for that liquor--but I'm sure as hell not going to ask them for it, and I'd be annoyed if my wife did too.
Now, if it isn't so much of a give and take relationship (i.e. all take), then yeah, I'd be annoyed.