Just now, I tried correcting a missing street near me, spent about a half hour playing around with the tools, and gave up. As OpenStreetMap gains popularity, I hope some of these companies using the data will devote some programmer resources to improving things so that "regular people" can contribute too.
What exactly did you find difficult?
To add a new way (OSMese for a linear feature of some sort) abutting an existing one, click where you want the road to start, then click where it ends. Congratulations, you have a new "way"! On the left give it a type, name etc etc. If you need to split an existing linear feature into two parts, click on one of the nodes, then click on the scissors to split it, then you can apply the correct values to each sub-section.
I might try some more editing later -- my first few impressions of it were just that it was too hard to use.
Never used it though.
I am really curios and heager to find out what would happen if more companies will start sharing their efforts with OpenStreetMap.
I would love to see the project getting some efforts and recognition from a larger community :) .. Who know what can start out of this..