I downloaded the demo of Intelliscore 5.0 and applied it to Scott Yee's rendering of "A Song Without Words". The demo converted a 15-second segment of Scott's MP3 file to MIDI, which I played back on my computer. No, the result did not sound like Scott playing, but the song was recognizable.
I remember back in the last century when some newbie would pop up on alt.binary.sounds.midi and ask for a .wav-to-MIDI converter. They would be ridiculed; the "experts" pronounced that there would never be such a product. I knew these "experts" were wrong and told them so (and got some amazing e-mails in reply).
How useful Intelliscore is depends on what you want to do with the MIDI file. It won't give our pros something they can use to entertain their audience with while they give their fingers a rest. But it might be useful for a transcriber as a starting point--either for providing a MIDI file or sheet music.
Even the demo version is useful. I guess you could transcribe a 15-second segment, and then apply a MID-to-Style converter on the result.