Yup yup I've used it. Pretty cool 'cept I can't ship parcel post (well, at least, to alaska... um...). I've been using PayPal shipping for a while before that, so it was still pretty familiar and I had the supplies (labels). I love that:
1) No need to be associated with a PayPal transaction...
2) No 15-dollar-a-month fee (stamps.com)
I think your problem was just a server fart... try it again today (or, later)
------------------
'87 Fiero GT, Automatic, 153k miles, stock everything, just trying to make it all work again.
Shameless self promotion: PIP giving you problems? Check out http://hostfile.org!