I used it for a year (parents own a farm in the middle of wales, they still cant get broadband!) and i found it made a considerable difference to my general internet browsing. Pages do load a lot quicker and you can set the level of image compression to low quality to speed it up more. Afterall this is what really kills 56k connections. As already stated downloads do not change at all, only things done via the browser.
Only annoying thing i found was that as it goes via thier servers you have to set your browser up to go via a proxy and every now and again it would just drop the connection for no reason, you then had to tell it to reconnect or if it still failed you would have change the proxy settings just to be able to continue. Not a hugh problem just annoying really.