They *just* launched, and they've been pushing a lot in University towns. I don't know how successful it'll be, but every single one of my friends has WS Cash, and if I ever had to send them cash I'd first ask if they'd use Cash since it's so much simpler than Interac.

Unfortunately, most people say no right now since the WS Cash Card is really weak (so no point in using it) and it takes a couple of days for you to withdraw money from WS Cash to your bank account.