I remember, when they first started touring live, Neil's voice was quite acceptable. But the classic PSB "Neil sound" was always that laser-like pure quality that instantly attracted me to the PSB in studio recordings.
However, the first hint there was something slightly odd, was the big South American "Disco-Very" tour, captured well on video. I remember being mostly impressed, but couldn't help noticing that Neil, especially in the slower music was often out of tune (not wrong notes), and his voice quality sounded rather nasally. Not exactly an appealing sound to my ears. It's a well known classical music phenomenon, that if you can't properly hear yourself as a singer or a violinist, say... you will subconciously help hear yourself by playing too loudly or slightly out of tune, so your ears can hear yourself. In live pop/rock music, this is why good sound monitors for the musicians are essential. Anyway...
Then there seemed a gap Bilingual came out about the time I renewed by interest in the PSB (I saw the Discovery Tour video later on). Neil wasn't bad at the Savoy Somewhere tour that happened around that time. Then there was the notorious gap. Poor Chris seemed to age 20 years within about two years, and nothing was released aside from the substandard "Screaming". And then came the CreamFields live concert, featuring some very cool new mixes of older songs, but with, IMO an utterly atrocious vocal performance by Neil: he was very badly out of tune, and his vocal quality was to be generous very poor. I heard many different bootleg recordings of the event, and I found myself utterly embassed to be a fan. It was then I decided that Neil, while superb in the studio, was to my ears unlistenable live. 1998-99 was not a particularly pleasant time to be a PSB fan.
This was redeemed by Nightlife, but I was dreading the live tour. The first performances were poor and then they became acceptable, but not overly so, IMO. The live video of the event is clearly better, because I think they had a chance to "tweak" it somewhat in the studio. Nevertheless, even when Neil was in tune, his live concert voice, on the whole was sonething I came to accept.
Today, I don't know if it it's just far more live experience, and possibly going to see a professional vocal coach (live singing is tough, even opera stars constantly go though this)... but 80-90% percent of the time his live singing is infinitely better (and I don't just mean auto-tuned). No, his laser-like vocal quality has returned too. I've not seen them live, but now they are superb live... well pretty much most of the time. I find myself enjoying that unique, effortless PSB voice that Neil has learned to use live. The improvement is dramatic, and it's easy to see why they love touring so much now. It's second nature to them now.

I just needed to get that off my chest... mission accomplished: and what a superb live act they are now!
-Zog