I'm going to kick myself for responding to GUEST, gargoyle: Your friend is an ignoramus and self-centered. I play almost entirely by ear now but I know what transposing is, I can find you a starting note if I don't know what it is offhand (which I usually do, since they're generally pretty predictable based on the key of the song), and I can handle my I, IV, and V7 chords just fine.

However, I took six years of piano lessons and only learned I, IV, and V7 by rote, without ever being taught why they were called that or what it meant in the grand scheme of chords. I finally learned that in about five minutes in an informal guitar workshop. Also, my play-by-ear string-band friends forced me to learn to transpose because I learned most of my tunes on dulcimer in D, and when I started playing with fiddles I had to start playing them in their correct keys. So, being able to read music doesn't mean you'll be able to do any of the above.

And learning to read at least basic music is not difficult. If you feel you're missing out, ask somebody for help.