I've replaced most of he external lights on my fun cars with led, mostly from superbrightleds.com. Based on the scientific tests of my and a few friends eyes, they appear to work well in most simple fixtures e.g. Rover Series, Defender, but not as well on my TR6. I will say, the super bright 45 led 1157's work great on the new MGB, and it's nice not to see the voltage drop w the brakes at idle.
Havent tried led on the gauges yet, I kind of like the dim vintage glow...