Gaming Paper is the latest innovation in roleplaying and miniatures accessories and is a low-cost alternative to expensive battlemaps and tile sets. It's an inexpensive, reusable and disposable product for gamers.
Gaming Paper Singles are 8 1/2 by 11 inches in size, and come in packs of 100.
Short Version: Great supplementary mapping tool for anyone that uses hexes.
For free-drawing maps, I'd consider the basic solution to be a dry/wet erase surface. You can use gaming paper for that, and I do like that it doesn't smear on me, but you end up paying more in the long run than a reusable surface.
But gaming paper shines in two areas: reusability and preparation.
Gaming Paper is amazing there's an area the party is going to visit several times, if you run the same adventure for multiple groups, or you're somehow organized enough to build up a library.
The big selling point for the singles packs to me is drawing out maps in advance. I can prep a night's maps or even an entire book of an Adventure Path and stash them for when I need them. With paper tokens, I can even get the tokens cut out and paper clip them to the appropriate map.
That isn't to say I never draw maps during a session, but predrawing means I can have the battle set up by the time everyone's figured out their initiative.