I became a 650B fan without even knowing it ! I got a pre-war Royal Enfield off EBay for £1, it was in a real mess with everything covered in black or silver paint. After a long search while the restoration was under way I finally found a couple of 26x1,1/2 rims which I laced onto some period hubs, it wasn't until I got the Michelin world tour tyres for the wheels that I realised that 26x1,1/2 and 650B are the same animal. I think they give a really relaxed ride with plenty of cushion effect.
Incidently the tyres that came with the bike were both "war grade" Dunlops, both totally shot but one innertube was in good condition so I re-used it for "originality". This size of tyre was popular on the old Royal Mail Post Office bikes.