I just discovered OSM recently, and I must say I'm impressed by the amount and quality of the data, and the ease of use and performance of the Slippy map.
I checked out some areas I'm familiar with, and was impressed with how up-to-date the maps are. OSM easily leaves the commercial maps in its dust on this front.
I also noticed some minor inaccuracies in West End, so I tested out Potlach. The end of Vulture Street had been renamed to Pigeon Street a couple of edits ago, I presume by someone with an unusual sense of humour. I restored it to its rightful name, and was fortunate enough to do it the day before the weekly update, so I got to see my correction on the Slippy map the next day.
This encouraged me, so I added some missing street names, and corrected and intersection that was shown as two disjoint streets. I'm a bit wary of messing up someone else's good work, so I only made the changes after driving by to refresh my memory and check that there weren't any recent roadworks changing the lay of the land.
There are more missing street names in West End that I plan to add. I'll also give JOSM a test drive, and see about installing my GPS software for uploading traces. There's so much to do, and so little time! :) But it's encouraging to be able to so easily add to a project of this magnitude.