I don't think those coffee machines are the worst idea in the world -- we don't have one, but my husband wants one. He is the only coffee drinker in the house, so making a whole pot is wasteful. He really enjoys one cup, and he won't drink old, stale coffee from yesterday. If he and I both drank several cups a day, a drip machine would make perfect sense, but for one cup a day . . . this isn't a bad idea.
Also, with these things gaining in popularity, I suspect we'll see the price come down as other companies begin to make the K-cups.
As for the general idea, gifts that require cost or maintenance in the future, I think it depends upon the circumstances. If it's something that the person really wants and will use, fine. If it's something that's just going to be a hassle, then it's an inconsiderate gift.
I bet we can all agree on the worst "gift that keeps on taking": A surprise puppy given to your child. That's the ultimate in rudeness.