This recent article on ispreview sums up for me the rather silly situation developing regarding these budget introductory unusable cap broadband services:
http://www.ispreview.co.uk/articles/cap/
Broadband should be about much more than just the occasional bit of browsing. You only need to visit a few sites with a bit of graphical content, or have a friend email a few photos to eat a bit of bandwidth. Do that just 2 or three times a week and you start to get close to these appallingly low and unuseable limits.
Do ISPs really think that all users want is lightening fast page updates. Or are these services really just to whet the appetite and entice newbies, who then will realise they've been conned and need to spend a lot more.