I think ASM is a great idea for "hacking", but the thing that doesn't make a lot of sense to me, is that you're usually only going to bother compiling to ASM for things which need the performance. The idea that they'll "still work" in non-optimized browsers doesn't seem too convincing -- games would probably be unplayable, and you'd see messages saying "This game only supports Firefox" etc.
I disagree. Granted, I'm an unusual case as I'm a compiler developer for a living, but my use of Asm.js would primarily be to write compilers for interesting or research programming languages to JS (granted, so I don't have to write JS). In this case the primary benefit isn't performance, it's having a reliable compile target that I can do profiling on. You wouldn't believe how important it is to have a stable (and well-specified) target language when you're writing a compiler.
I disagree. Granted, I'm an unusual case as I'm a compiler developer for a living, but my use of Asm.js would primarily be to write compilers for interesting or research programming languages to JS (granted, so I don't have to write JS). In this case the primary benefit isn't performance, it's having a reliable compile target that I can do profiling on. You wouldn't believe how important it is to have a stable (and well-specified) target language when you're writing a compiler.