Tucci, I deal with your problem, but from the other side of the console. But I HAVE dealt with it from your perspective too.
I cannot express strongly enough the need for involving other people in your production. Having the opinion and encouragement from someone that you trust shares a little of your artistic visions is invaluable in the recording process.
How do I know when I just recorded the perfect take? Simple. It moved me in the way that the song moved me when I first wrote it.
How do I know when a client I am producing has just recorded the perfect take? Well, it was usually within the first 4 or 5 takes, and they didn't mess it up too bad....

But really, it is when the take contains a certain energy and character that says to me "LISTEN TO ME!!!!".
But my good friend, I have to tell you, I don't know that people always know what really sounds good and what doesn't. Let me illustrate.
There is a song on my website (I won't say which) where the band insists that the backup vocals are in tune. I insist that they are not. I have played the song for other musicians and engineers that without me saying one word about the vocals who pop up and comment about the backup vocals being out of tune. It is evident to everyone but the band. Those who can't describe what they think is wrong with the song just say something like "I just don't care for it" or something like that.
In other cases, I have worked with musicians that write 5+ min. tunes that are as boring as hell, but the second you suggest shortening the arrangement to make it a little more exciting, they insist that the arrangement is exciting and that they want to add some more parts and what not. When I try the good old stand by of "most radio tunes are less then 3.5 mins long", they come back with, "not Tool's tunes, and they are big time"....*sigh*........ Of course, these bands never sound anything like Tool, and for that matter, the drummer of Tool can probably play guitar better than the guitar players of this band can....
Other examples.
I have worked with I don't know how many singers that will want to redo a take because they mispronounced one word in the take. Usually, the offending word sounds pretty damn cool. I tell them that and they look at me like I am crazy. So, they do another take that lacks most of the raw energy of the first take, but they pronounced everything good. Big deal. David Lee Roth of Van Halen messed up stuff all the time and sold it! He made the mistakes sound good. That is what is important.
All the time when I am producing bands do I have to show them that they are not really tight at all, even though they think they are tight. It usually takes throwing the song on tape, then soloing like the kick drum and bass guitar, or getting them the listen really close to some breaks where everone stops playing. It usually takes them about 3 or 4 listens before they actually hear it. I heard it the first time. They where all prepared to go with a take that wasn't very tight.
Anyway, I only listed the above to illustrate that not everyone possess's the ability to really "hear" good musicianship and good takes in the studio. That is why producers play such a big role in music production. They HEAR music well. They have a unique talent for hearing where good musicianship and good artistic expression come together and challenge the musician to achieve a better take then what the musician would settle for.
A big challenge for the DYI person is that they don't get the benefit of hearing what they are playing while they are playing it from a listeners standpoint. Often too, the musician is not capable of being objective of their take. They are listening to so many other things, but not really just sitting back and asking themselves in a really honest way "would I like that if someone else wrote and performed it?".
Most of the best recording musicians I know possess a few things that other musicians who don't record so well don't.
A great sense of timing and a seemingly intuitive understanding of complex rythm.
The ability to vocally harmonize with most anything they hear.
The ability to improvise with many genre's of music.
Without these abilities, I just don't think a musician is as suited for the recording environment. But that is just an opinion that has a few exceptions, but not many.
You want to know the best way to know if you just recorded THE take for your song?
Don't listen to it for a week. Play it back a week later and ask yourself if it was something that was done well from a listeners standpoint. Forget that you are the artist and just listen. You will either get better or you will quit music if you do this honestly.
Ed