A mother whipped this out in a restaurant last night so we asked her about it. It's the TinyDiner Portable Placemat from Kiddopotamus and she likes it not just because it makes post-dinner cleanup with her 10-month-old easier, but because she doesn't trust that the restaurant table she's plunking food down on is clean to begin with.
The TinyDiner suctions to the table and has a built-in scoop at the edge to corral runaway, flyaway food. The mat rolls up into a tube and fits in a large purse or diaper bag.
Available in pink, green, yellow or blue, the TinyDiner is sold for around $10 at many big box stores (Toys "R" Us, Babies "R" Us, buybuy Baby) as well as online from Amazon or these specialty shops.