After carefully following all instructions, the installation appeared to go smoothly but when I click on the test link in my preferred browser, Safari 4.0.5, it immediately pops up with a fail message. Fortunately it appears to work fine in Firefox. Given that Snow Leopard has been out for over six months now it's disappointing that Snapper still don't appear to have properly tested their product with it, but it's not too much of a hassle to switch browsers on occasions when I need to do a top-up.
I just thought that this might be useful information for anyone who is considering getting a Snapper USB. Any comment from the Snapper team would obviously be very welcome.