First off, the UN hasn't said that the strikes violate 'International law', just a UN official. A fine distinction but an important one. In reality, it will likely go nowhere, even in the UN.
Jane Mayer has a good article on this in the 26 Oct New Yorker. It's subscription only and I'm iPhone only so I'll be brief. The concern with these drone attacks is that they're conducted by the CIA with little oversight, and the scope of these killings has been broadening. No doubt we're comfortable launching a missile to kill bin Laden, even if a few others are killed. But are we comfortable with the 16 missile strikes and 200-300 people that were killed in our hunt for Baitullah Mehsud before we finally got him? What of the 50 drug lords suspected of financing the Taliban that were added to the pentagon's list of approved targets? Are we going to target Karzai's brother too?
Don't look at it from a technical standpoint of UAV's replacing piloted aircraft. They're a substitute for CIA assassinations, and were conducting them to an unprecedented degree.
From what little you say I think the author of the article is almost certainly very limited on what she knows about the strikes and who is targeted, along with who gets killed in them. Very few people really have the full picture of that effort, to assume that it lacks oversight as well as making assumptions on the targeting and employment parts of the picture is incredibly naive, arrogant or both. I think that too many of the people who criticize the effort and other CIA efforts/operations today still cling to the Church Committee and Hollywood versions of how the CIA does business.
I think a more pertinent historical analogy would be Laos during the Vietnam War, where the enemy uses an international border to facilitate it's operations and as a safe haven. Make no mistake, these guys getting killed are legitimate military targets, killed during ops that are not conducted by the US military due to a myriad of concerns but military targets none the less. Calling them assassinations is a stretch, even for human rights types. The 'collateral damage' piece is sticky but from what little you talked about the article I would say the author is way overstating them. Otherwise there would be much more outcry over them, which has been surprisingly muted for that region of the world. Simply put, it has been very impressive and effective effort.