Much like the rest of you, use by dates are of little concern to me when it comes to beer (within reason), but I found a few bottles of Goulden Carolus, which is 9% ABV and bottle conditioned, in the back of a cupboard a while back which were around 14 months past it. It tasted fine, but it was only when I tried a fresh bottle a few months later that I realised how much the beer had deteriorated. 14 months is quite a while, but I would have hoped that a stong beer such as that might have aged a little better.