Agreed--these guys have been around for quite some time. I do think they are really just starting to take off though. I just got my reader about 3 weeks ago (It had been on order for almost 3 months).
i don't think they started actually shipping large quantities of readers until recently, though.
In any case, if you're freelancing and want to accept card payments, it's pretty good. I'd been doing a project and had been using an authorize.net processor, but square is cuter and, more importantly, has much lower processor fees than most other places with not even half the overhead (i.e. crazy account setup/maintenance fees/etc).
I noticed problems with their card reader when using with an ipod touch, but on the iphone, it's been pretty good.
