What do you think of 'em? I only have one so far (Warp's Edge), but it is cool. Being anal about alignment and symmetry, mats are awesome for me (even though I only have one). Having a "background" to the game space is very nice, too, since my table and/or tablecloth are boring and anti-thematic, as well. But, the mats are also 'space consuming' for storage, which has to be considered by me, anyway. There's also the cost, of course.
They seem to have too much of a "profit margin", too, but I think they're praying on us gaming addicts. But, probably a good marketing decision, though. Damn corporate bastards! They know us too well.