been using it for a while now... about a month...
it works fantastically well, i use it to make free calls at home, school and work, and if you ask for more credit, they give you more for free (until they sort out their systems to accommodate buying credit in real time online) and with that credit i can call home to the UK. it's really been helping my phone bill, and my clients in the US who have mobiles that have free national calling (most of them) can call me for free on my truphone (+1 310 based) number.
great stuff, i wish there was more insight into where this technology leads, though.