Embargo is rapidly becoming one of my favorite cards. I think it's the most interactive card in the game - more than any other card it force you to pay attention to your opponent's strategy and figure out what you can do than will hurt him more than it hurts you.
You also have to be careful that you don't lock yourself into a strategy that can be countered with an effective use of Embargo. And you need to be flexible to adjust your strategy every time Embargo is played.
Then throw in figuring out when it's worth it to pick up a curse for that card you need.
(A special case for all this is Potion cards. The second someone picks up a potion you should think about ignoring the potion and grabbing an Embargo to Embargo the potion card you are sure they want. It's likely still worth picking up a single Familiar if there is an Embargo on it, but likely not worth the second one. Most other potion cards are at their best when stacked - and that's the hardest thing to do with an Embargo'd card)
Here's a fun game I played where we both played pretty well. There ended up being 8 Embargos played on 8 different cards - and five curses picked up between the two of us.
http://dominion.isotropic.org/gamelog/201210/10/game-20121010-113700-5a039b29.htmlSmuggledDuchy opened with FG, so I ignored silver and grabbed an Embargo to block his spamming of FG. It just went on from there with Embargoing of Potion cards, Golds, Provinces, Border Villages (when I was buying BV+Duchy and then Remodeling BV into Provinces) and on and on...
Ed