<declaration of interest>I work for an ISP (Houxou.com)</declaration of interest> and I see the same things you do from a slightly different perspective, though I feel as frustrated as you do. [these are personal opinions and not of my employer blah, blah...]
First - remember that it is very important to distinguish between BT Ignite (a part of BT plc which provides the ADSL service wholesale to ISPs) and BT Openworld (who are an ISP wholly owned by BT plc.). They both seem to have appalling service though - you saw what BT Openworld are like, and we hear that regularly from people who ring us up and would like to change provider - which is sadly impossible within your 12 month contract.
There are so many other ISPs (not just Houxou) around who absolutely cane BT Openworld in all areas - service, speed, reliability, value-added services, and the all-important fixed IP addresses, that there is no reason for anybody to deliberately choose BT Openworld unless they are uninformed. Unfortunately it is very easy to accidentally fall into BT Openworld's arms as many people do not understand that other ISPs can offer this service. For example, i have dialled BT's consumer number - 150 - a number of times and enquired about ADSL. Each time I end up being put through to BT Openworld - I am pretty sure this is not supposed to happen. A cynic might say that a certain amount of effort appears to have been made to cause confusion and make access to the full picture difficult for consumers and SME's alike. Yes, I am one of those cynics.
BT Ignite on the other hand seem to think faults should be resolved at 'telephone speed' and not 'internet speed'. They have no appreciation of the way ISPs (the good ones at least) handle technical support which is ASAP. We don't pass things on to some technicians desk to get looked at the next day - we get them sorted right away if possible.
However every fault we raise with Ignite takes a minimum of 24 hours to resolve, and it can take weeks! When you speak to them on the phone you are shunted around, promised phone calls that never materialise and you are never allowed to speak directly with engineers working at the exchange. Often, they will send out engineers to our customers, even though we are 100% sure that this is unnecessary and that the fault lies in the exchange. Such a visit delays a resolution by up to 48 hours. Many problems could be solved in less than an hour if we, the ISPs, could speak directly to technical people within BT. An escalation manager in BT recently told me he considered 24-48 hours a perfectly reasonable length of time for a fault to be resolved. Wake up and smell the 21st century!
If only they had some management prepared to stand up and be counted and make some radical changes! But they don't seem to, and their corporate culture sits on innovation and change - people enter the company intending to make changes and one year later are faced with the same intransigence as before.
We have corporate customers who understand they are not paying for a leased line, but rightly expect a perfectly reasonable level of service. We can't give it to them because BT Ignite can't keep up with all this new-fangled internet technology, and we get stuck in the middle looking as if we are making excuses (Customers are not allowed to communicate with BT directly). Reselling BT ADSL is frankly an embarassing experience. We have to put so many of our resources to use fixing installation problems (> 50% of our installations have been messed up in some way by BT) and other failures which crop up that we don't have time to market our proucts to new customers, which is partly why ADSL hasn't taken off like it has in the US, Canada or Germany.
Of course, unlike ADSL providers in other countries, BT refuse to provide SLA's and compensation, which gives their employees absolutely no incentive to get anything done... Until they do, many companies will refuse to get involved, and continue paying ludicrous leased line and ISDN charges to - guess who!
When running ADSL is great, and since leased lines and ISDN are kept artifically expensive (also by BT), ADSL is still fantastic value. But with no effective nationwide competition, and limp-wristed inaction on the part of OFTEL, do you really expect Ignite to ever make the effort to improve things?
Of course there is one other point - nothing to do with BT - which explains why there are so many complaints from customers about internet access in the UK in general:
What do get if you want cheap services?
ADSL is a very low margin product. If Internet users in general can be shaken from their mistaken belief that everything can be free, and that cheaper is better, it will be much easier for people to roll out expensive technologies like ADSL...
BT OpenWorld charges £40ish for a product that costs them £5 from BT Ignite. That's £5 per month for 512k bandwidth and tehnical support amongst other costs. Do you really expect to be happy with using that service? Most other ISPs charge at least £50. I rest my case.
My advice is: get a decent, committed small/medium-sized ISP who can offer friendly, well-informed support, pay for what may not be the cheapest service on the market, and be prepared to suffer at the hands of BT's fault resolution processes.
UK broadband is not going to kick off the way it should unless OFTEL takes a harsh stand against BT (which is almost certainly not going to happen...)