My question is how does this help them if the only chords they know how to play does not fit their voice range or the voice of the person with them who is doing the singing? I agree it is great to be able to call up a song that is in the key of (place key here) and to be able to play it. Gives you a feeling of accomplishment. I think that if one learns SEVERAL simple basic progressions (leave out the key of B or F and any of the flat keys) a whole different world then opens up for you. Then learn how to transpose a song to a different key or the proper use of a capo and you can open up the universe. This tool (search by chords) is a well thought out item but don't limit your learning of playing by depending on this as the answer to you becoming a GUItar GOD.
Nela
I think for some the felling of accomplishment comes from learning to play any song. If you learn a Em, G, C, D song then why not try to learn six more with the same progression. That way you can get more playing under your belt in a shorter amount of time because you already know the chords.