I just wanted to suggest you might like to use Google ads instead of "click here to sponsor this area". At least while your popularity is building up, the Google ads are easy to install, and you'll get a little income from them. I'm guessing that the sponsorship is slow to come in at the beginning. I have Google ads on a website I maintain and I get a fairly consistent income from them. My site has like 2000 hits/day and I get around $8-10/mo from it.
It's a reasonable suggestion, and I may do it. I'm actually working on a mobile app at the moment, and the plan is to include the iPhone equivalent there, so that may push me to do it on the site, too.
The note that's there now is a remnant of my previous hope that I could get local bike shops to sponsor the site. That turned out to be more complicated than I thought, so your suggestion is probably a good direction to take instead.