Personally, not had a problem - engineer arrived on time (actually early, which he'd called me beforehand at work to ask if it was OK, giving me enough time to get home).
However, am currently trying to migrate a non-BT ADSL line onto an infinity business product and am scuppered by BT not being able to find the address. Now this is not entirely BT's fault, and the chap I'm dealing with has been very helpful and has patiently spent quite a while on the phone to me as we try plugging all sorts of things into their database, but does show that their computer systems clearly don't have a clue.
The issue is that the property is a pavilion on a sports ground, and that the billing address for the existing BT phone line is our main business location and not the address of the sports ground. But their computer cannot cope with this. If we book an engineer, he will turn up here, at the billing address, and not at the location in question. There is no option for 'send engineer to X'. Because the location doesn't appear to have any sort of valid address that matches what is on their computer, we can't go any further. It's rather surprising that BT can't look up oh, I don't know, the unique phone number currently installed and see what box it is connected to. You can actually see the BT exchange 100 yards away in a straight line.
It does make me wonder what would happen if we stopped paying the phone bill. Clearly they couldn't disconnect the line as they don't know where it is...