After having played over 3000 games on Iso, every once and a while I still run into something I'm doing for the first time.
Just a couple of minutes ago, I played a game with University and Vineyards. There was another interesting card: Remodel. To win the Vineyards split 6-2 and end the game, I remodeled a University down to a Vineyards. I don't remember ever Remodeling a Potion card down to a Vineyards before, but it was certainly a neat trick. Remodeling down doesn't happen very often and this may have been my first at that too.
It just amazes me that after so many games, there are still things I do for the first time.
What are some of your memorable firsts? Obviously beginning players will have a lot more firsts, but feel free to post anything that you found interesting.