To be honest if they were open about their new network when it was clear it was in the planning stage, I would not have left plusnet.
At the risk of letting the cat amongst the pigeons, why should they?
They are a business who have a strategy, plans and are probably more than aware of what is right/wrong internally. Some things they can share, others they simply don't want to. It seems like because we have Twitter, Facebook and forums that people seem to think they have the right to what might/can be commercially sensitive stuff for everyone these days.
The Plusnet forums are rife with it, you only need to look at the new network thread and the same people coming back asking for rollout plans, dates, times and then coming back asking for updates!!! It's crackers.
In answer to the original question though, I'm with Plusnet and I've had a great run with it since I joined.
I left Virgin media as I work from home a lot and had years of issues with VOIP, VPN and just general slowdowns. You'd call, get a couple of quid credit and same again the next night.
I've got the TV, 76/20 package and use my own router - I don't recall a single day of downtime the in over 2 years personally. I recently called up to renew my package and get a discount again and was through in about 5 minutes, which looks to be unusual.
No experience of the fault process, as I've not had one. The only thing I'd not enjoy is if I had a line fault and got the same Kelly engineer who done my install.
Never used ZEN, so can't comment on how they compare.