Strikes me that there must be a lot of local variation in, well, something, because although I'm quite happy to whinge about bits of the service round here (SE London/NW Kent), it seems fundamentally OK.
My experiences are clearly at odds with those of other posters, but I'm reasonably happy with everything from finding convenient sessions to making appointments and being seen in a timely manner. The past couple of sessions, it's been about an hour from walking in to leaving, having eaten my fill of biscuits; the session before that took a bit longer, but that was down to a backlog caused by about three donors in a row having health problems which meant they each needed an extended phone consultation with the offsite doctor, and meantime were occupying the privacy cubicles so no-one else could be processed ...