I've used it in the past. Some say it's one of film photography's best-kept secrets! It does, indeed, give excellent results. It's also cheap and easy to make and keeps well. I found it gives better highlight definition than D76/ID11. The big downside was that you generally have to give a film at least a full stop more exposure than box speed. I usually rate HP5+ at 200 anyway so that's not a problem for me but it may be for some. The only reason I stopped using it was that I was given several unopened 5 litre packs of ID11 and 2.5l packs of Perceptol. When I've used these up I may well go back to D23.
It's also the first bath in some 2-bath developers such as Stoeckler's which works really well for high-contrast slow films like PanF+.
http://www.film-and-darkroom-user.or...ight=Stoeckler