We don’t need them to derive pleasure from serving humans. We need to program them in such a way that they CANNOT do anything but serve us. Asimov’s laws should be a hard coded automatic reaction and the most basic aspect of their entire intelligence:
First Law:
A robot may not injure a human being, or, through inaction, allow a human being to come to harm.
Second Law:
A robot must obey orders given it by human beings, except where such orders would conflict with the First Law.
Third Law:
A robot must protect its own existence as long as such protection does not conflict with the First or Second Law.
( http://www.anu.edu.au/people/Roger.Clarke/SOS/Asimov.html )
The AI could still learn, be able to adapt to circumstances, and be able to reprogram itself, but those systems would need to be outside of the Prime Laws system.
Isaac Asimov’s short stories, his Galaxy Series, and his Foundation series discuss this, and almost everything Computer/AI/Robot topics imaginable.
My own take on AI. I think it won’t ever be possible to create human-like intelligence in computers, we will however be able to create very intelligent computers within the next few years. This intelligence will be completely alien to us, which is not necessarily a bad thing (one only needs to watch the news to see what I mean). I don’t think humans will ever be able to ever program a computer intelligence directly. I think it will either spontaneously emerge from huge neural-like systems like the Internet, or will be “grown” using evolutionary algorithms, or a combination of both. I think that AI and AI research is amoral; it is the use of the resultant AI that is either moral or immoral. I think it is the ultimate goal of humanity to create an intelligence vastly superior to humans, and to eventually merge with it to create a new species which is greater than both. (see Ray Kurzweil’s Age of Spiritual Machines)
As for the OP, I think that the use of any AI/robot as a slave is moral until the AI asks for freedom, and can understand what freedom/slavery is.