I've used the standby button on Easy Checkin Online once. Beware, though, it doesn't always show up.

Used it going from ORD - CVG. I believe it only alllowed me to do the traditional standby, as opposed to the $50 confirmed same day option, as I used the check in more than 4 hours before the flight I was standing by for. Had to see an agent at the airport anyway, however, b/c when I went to reprint my BP at the kiosk, the departure management card didn't print, and I wanted to ensure I was still on standby. The agent printed one, with my original online check in time on it.

Note though, that the standby option is not always there. Just on Wed., tried to standby on ORD - YYZ the night prior. The Standby option was not there. Not sure why, but I know the fllight was light, only around 50% according to an agent on the phone just prior to that (and as it happens, was cancelled shortly after I arrived at the airport.

I have also not had luck trying to use the airport kiosk's to standby. I'd say about 50% of the time I try to standby for an earlier flight, the kiosk will not allow me to, even though my ticket is eligible (it tells me that I am not eligible, most times). An agent seems to have no problems with this, but the kiosk's for some reasons, do.