bokEck,

I understand what you mean about the empty space on either side of the cards in landscape mode. I had the same thought myself, that there is a lot of unused space on either side, and tried a few things to see what would look best:

1) Increase spacing between cards - When I tried this, it looked just plain weird. The eye is immediately drawn to the gaps between the cards and you find yourself asking "Why is there so much space between the cards?"

2) Increase width of cards - With wide cards, they don't look like cards as all as they are too fat. If you increase the width, and there is not enough screen height to increase the card height as well, the cards look fat.

So, overall, a gap on each side seems to look best. Feel free to experiment, and post some screen mockups here if you like.

Thanks for your feedback!