I found this kind of interesting. I was looking at the decks that have been registered so far and did a search to see how many of them contain the same rare cards I have in my deck. At the time I checked 9287 decks had been registered so far. Of the four rares I have in my deck, each showed up in 2.42%, 2.36%, 2.28%, and 2.43% of the registered decks. There might be a couple of conclusions that can be drawn from this. One, rares seem to be rather rare. Two, FFG's distribution of rares seems to be pretty consistent (for this sample at least). Three, at this frequency, for the number of other decks I might come across I might never see another copy of "my" rare.

By your own estimation, that's a little over 1 in every 50 decks. If 10 people show up to play sealed events on a weekly basis, that's 1 of the same rare every 5 weeks or so.