This thread also prompted me to have a look at my history. Started with Zen in April 2003 as soon as broadband was available to me, went with Zen due to a friend's recommendations.
Started on ADSL (I forget the initial speed) then onto an 8Mbps service (getting around 6-7) and then last year up to 80/20 FTTC, getting around 76Mbps download as cabinet very close by, and switched over my phone from BT at the same time.
I've not had to call on tech support too many times, but when I have I've found them efficient, knowledgable and certainly not reading from a script! One phone call has usually sorted out any minor issues. I've found the connection has been very reliable and stable, my main reason for going with Zen in the first place.
My most recent contact with Zen was regarding single thread congestion
and was solved very quickly after contacting Jon Green on here.
So for me it's been 14 years, but no mug!