Mixed experience. I signed up for the Pipex ADSL deal - £19.99 plus VAT. Self-install - well, I can plug in a modem and some filters with the best of 'em.
It went live when they said it would, and the speed was stunning. Then a week later it didn't work, and I discovered that:
1. Contrary to rumours, Pipex has no call centre. It's a myth. There's a telephone number but no humans at the other end of it. I tried weekday daytime, evening, weekends, even at 3 am. Always the same.
2. You can enter your query on the Pipex website (using your dial-up modem and your old ISP), but nothing will come of it. I know - I've sent them 14 queries over the past 8 weeks, and not one has been answered. Not even acknowledged!
Anyway, eventually some helpful webpages gave the fix. I'm glad I kept the dial-up facility!
So - go to the newsgroups, and you will find experts better than any the ISPs have. These fine folk will answer all your questions, tell you where to get the revised drivers or software or whatever, and get you back in business.
Oh - and I applied first for Demon ADSL. The nice lady said she'd call back in a couple of days when they'd tested the line. That was January. Not heard yet...