I've used it maybe... twice? Back when the game first launched, I played around with some randoms. I think it's a fantastic feature, but I have yet to make use of it.
I gotta start using it more, especially since I faced a rare Akira player last night and had some fun matches. Would be great to finally have a training partner : D
Which reminds me....... I STILL need to send a throwdown challenge to someone D: Would anyone care to volunteer for a Simple Match throwdown later on tonight? <.<