I don't sing, so that's not a consideration for me personally.

When I'm learning a new song, I'm usually very excited to start playing it, and I'm too lazy to transpose the dots. So I end up learning it in whatever key it's written. That might change if I can successfully make the transition to an electronic score display program. But I have so much paper music!

I agree with Bill Lewis- I'm sure I could recognize and memorize patterns better if I transposed everything to C. In the long run that would probably allow me to play more songs from memory, leading to fewer mistakes.

Again, the key enabler for learning new music in a specific key is transposable electronic score sheets. I even bought myself an iPad for this purpose. But so far all I've used it for is to display scanned images of paper music sheets that I already had :-(

Getting a little off-topic, but one thing holding me back... With an electronic score display, how do you add annotations to the score??