The best possible results are still from micing up real cabinets, so ideally that's what you'd probably want to do.
That said, not everyone has the opportunity to mic up and crank an amp for hours on end to record.
Enter emulation and impulse technology. Soundwise it can get you 95% there, in less than half the time, without having to crank anything. To me this is the ideal solution for those who want to record quick ideas without too much hassle, and those who can't afford, or otherwise aren't able to mic up a multi-thousand dollar setup.
Impulses can get you 95% there, which is enough to record nice ideas, and make a demo. When you get signed (as if right?) you'll probably have access to a recording studio, better gear, and various other options not available to you previously. This is where impulses begin to take the backseat to real micing, because you now have the means, and the opportunity to do real, high quality mic'ed recordings.
That said, I think there is far too much emphasis on that amazing gear, that amazing micing technique, those amazing impulses lately. I see 15 year old kids with a god damn ENGL SE and Mesa 4x12 cabinet. Incredible gear, and if those 15 year olds worked and saved up for it all the more power to them.
However, more often than not their skill is greatly lacking. The songs they make are uninspired and the playing itself is sloppy. I don't care how great their gear is, I don't care how incredible their sound COULD be. Tone, and music is mostly in the fingers, and in the mind. I'd rather listen to inspiring, refreshing music thats well played but recorded with impulses, than listen to the so called real deal mic'ed up recording with uninspired sloppy playing.
Don't get me wrong I don't mean to bash 15 year olds. In fact, I know a 13 year old who royally desecrates my ass when it comes to guitar. I'm just trying (and probably failing) to say that if it is well played, inspired and fresh it'll sound good, even through mediocre gear and recording.
Where was I going with this? OH YEAH, I love chocolate...mostly dark chocolate with nuts.
/end my unadulterated opinion