maybe we can use this thread for collecting those. Just will start with one:
Pressing spacebar while mousepointer is over an area in deck editor where a bunch of cards is listed (either in cardpool, deck or All Cards) shows the listed cards in tiled view. Could not yet find any place where this is mentioned as a feature (but nice feature :D).
Just post your findings below.
Holding ~ while mousing over cards (on the table, in the deck builder, etc.) will display the card's full textual info. It's handy when images are low-res, out of date, or in another language.