I haven't heard anyone mention this -
I use a large square of velvet - usually dark blue or purple. I've found that cards tend to slide on silk, but they stay put quite well on the velvet. Additionally, I have short nails and so the extra loft helps me turn the cards over easily. Also, I love the feel of velvet and it's elegant rather than witchy (I like to be subtle).
I prefer a solid, dark color because it doesn't interfere with the card images - in fact it makes them pop out - especially if you've cut the borders off your cards.
I buy a piece where the length is just slightly longer than the width. Since the selvage is finished I only have to hem two ends (if at all) - which then makes it square. If you get a lighter weight washable velvet that's not too wide, then it packs up pretty small for travel and provides a good wrap for carrying breakable items.
I also find that my velvet square makes a great "instant altar". By using the aces to represent the four directions I basically have everything I need for that spur of the moment ritual.
I find that using a spreadcloth immediately defines a "sacred space" where something out-of-the-ordinary is going to happen.
Mary