I've just got in from seeing him in Buxton at the Opera House (I also bought one of the 5 signed canvas's).
Personally I was very impressed, I've only seen Jack live last year at the Colne Blues Festival where I stood at his feet the whole performance.
The sound after about 2 songs was spot on and I loved the way he started the show, with him on keys and him slowly shifting to bass as the band came on stage.
I had a great night and really enjoyed it and would say he was probably better than he was at Colne, but it wasn't a flawless performance, I think I heard the intonation off a bit here and there (No way on earth I could do better though) but his vocals were AMAZING and his piano/keys playing was also superb.
One thing I will say is I managed to catch him before he left Colne last year and he refused to shake my hand as he said he had terrible hand cramps and he just about managed to sign a book for me. Knowing this, the set was structured in a way that I could see this trying to be avoided, couple of songs on bass, couple of songs on keys, couple of fast songs, couple of slow songs, couple of fast songs with other bass player doing the heavy lifting and then big finale of Sunshine with a gap then the encore of Politician.
I would agree he's past his prime (his prime being sometime in the late 60's early 70's) but hes better than a lot of the early 90's stuff I've been seeing on youtube. End of the day the guy's 68 and he can still play circles round most people and while I love his playing, being a bassist is only about 25% of JB with a huge chunk going to his voice which HOLY HELL is just STUNNING.
I'd say if you can go check him out, as he really is a legend.