I will preface this with a note that I have only put my music out online, and only for free on sites like Soundcloud.
I have my tracks start almost immediately - don't cut it too close though, you can leave a little bit of space at the beginning - I found early on while recording that if I cut it to the almost exact instant of the beginning, it would sometimes get cut off when played.
Then I leave space at the end of the track. I don't like to let the computer add time between tracks, I'd prefer to do it myself. On the Mac, it asks if you want to add 2 seconds between songs, I always say no.
Good question about how people listen to music now. CDs seem antiquated now, though I am sure that many people still listen to them, myself included. I think it's partly age-related and what people are familiar with, and also convenience related - on a recent 6-hour drive I had a bag full of CDs, but having everything on an mp3 player would probably make sense, especially if that's how it was purchased.