I made a somewhat interesting discovery while following soldyne's tutorial "Making Money the easy way". While building my rural suburban area I used the roundabouts from the NAM to connect my avenues, while following all other steps of the tutorial to the letter. I did not get any growth in my suburbs at first. I kept the game running for a couple of months, but the "popcorn effect" did not start. In the end I replaced the Roundabouts with regular avenue intersections, and almost immediately my Sims started moving in. This could of course be a coincidence, but I thought it should be noted.