That's a bit of a problem. We had a very high ranking position on that term #5 or so. Then we suddenly dissappeared on every single term. We're trying to get in touch with Google on this issue - just to make it clear - we did no spam / blackhat.
We track our search term rankings daily and they frequently drop off the frontpage google results for a day than come back higher up or at the same rank the next day.
Google is constantly testing sites and seeing which ones perform well.
I wouldn't be worried unless its still not back in 2-3 days.
Think of imitation as flattery. It also gives you a chance to think about whether your competitive advantage is easily duplicated. And I mean that in a positive way. Really nice site. =)
