Hey Kerry,
Wasn't it Lester Young who said that he always learned the lyrics? I find that if I know the lyrics I keep the form together much better. Then if I get to play a solo I can try to phrase as if I was singing, rather than "G minor 7th = Dorian, C 7th = Mixolydian. . . " I always tell my students to try to get at the emotional tone of a tune before they solo on it, and lyrics can clarify what that is. Some meanings aren't always obvious through the harmony (Major key = Happy, Minor key = Sad), -for example: "Makin' Whoopee" gets downright cynical in the third verse.
One problem I've gotten into though is that singers often get the words wrong, and I have a DEEP need to correct them ; ) I've since learned not to do that though...
Has everybody seen
http://www.kissthisguy.com ? for misheard lyrics it's a real hoot!
Another key to learning tunes is to be able to feel four and eight bar phrases without counting. . . I'm sure everyone can remember learning "So What" and forgetting which "A" section they were on. Also important is to remember where the bridge goes (usually the IV chord, or III/VI/II/V in standard tunes), and remember any little modulations that might happen.
Laurence