"there's no escaping the possibility that one person's happiness might not be the same as another's"

I think that happiness comes to people through different means e.g. their career, family, travel, etc. I would even say that people can desire different "feelings" of happiness i.e. pleasure, euphoria, eudaemonia, etc. But I think it's not too far fetched to think that you can roughly figure what actions produce what feelings and what people enjoy what kind of feelings. If that makes any sense?

I actually do think Utilitarianism can be useful on an individual basis. It typically boils down to "do what makes you happy." Once you have harm being formed as a trade off things get tricky. I'll try and go into that in a second.

I don't like the idea of aggregating happiness. Here's the solution I agree with most: if you have 6 dying patients who need a drug and 5 of them can survive with your supplies while the last 1 needs all the supply of the medicine ensuring the other 5 die. What do you do? Give it to the 5 or the 1? Intuitively you say the 5 because it saves more lives and provides more happiness. However, happiness is only valuable to a person perceiving it. Assuming these people have no family or friends then each person surviving is only providing happiness to 1 person each. So each life being saved totals out to 1 total happiness gained to the person actually perceiving this happiness gain. So the idea presented is that if we want to maintain some sort of justice (which if preserved tends to produce more happiness in the long run, generally speaking) then we should weigh each person equally. So what we should do is....roll a dice. Leave it to chance. While the odds do favor the 5 (if you roll a 1-5, you have but no choice to save the other 4) it still allows for the 1 to have his chance to survive. If my explanation wasn't clear, let me know.

Also, what do you mean by utilitarianism accounting for desert? What is desert?

Thanks for the reply!