Hmm... weird... ok thanks all... My daughter is the one that started a game yesterday, and she told me she got a weird "install" message and had to wait for a while before the game started (she is 26 btw, so knows her way around computers)...
I find this a little strange... I get a feeling that the game somehow got unistalled, and steam detected that and forced a full downlaod and install... but for the life of me, I can't figure out what would have caused the uninstall...