WOW! People are still debating this. Honestly my opinion on whether "Perfect Pitch" is worth obtaining. That is a question you should ask yourself, I believe as a musician: it is worth a look. Afterall, your overall musicianship (whether your transposing your favorite songs, or writting your own songs) is based 100% on your ability to hear. You have to hear it before you play it and be able to recognize what it is you hear to learn it. So I would think at least learning the sound of 12 notes would help tremedously. Your call.

The best way to learn notes is to sing them as you play them*. Say you play a C, just sing in pitch with your guitar. For some reason, this method will implant the sound of the C in your mind very naturally. And just go on til you learn all 12. Josh, I see you said that you knew the sound of the important ones, well why not just learn them all. If you can learn a few of them, you can learn them all.

*Note: Play notes around the middle C range, the pitches are much easier to hear in this spectrum. As you go lower they become muddy (bass players know what I mean), and the higher you go the more fragile and tinted they become.

This is still not Perfect Pitch, cause that is a far broader range of perception. This is just what most people are really after, and it's a invaluable skill to know all 12 notes.

Also, just another note here is a small list just off the top of my head of people who have Perfect pitch: Frank Sinatra, B.B King, Miles Davis, Tommy Mars, Eric Johnson, Yngwie Malmsteen and countless classical musicians.