I'm living in the suburbs of Pretoria, OSM showed a Woolworth store that according to the security guy hasn't been there in 3+ years :D
Because the map "looks complete" Pretoria hasn't really attracted many mappers since his departure.
Cape Town has a much more vibrant community of mappers. I've also been able to get crazy high resolution aerial imagery for CT from the municipality which helps: http://coct.aerial.openstreetmap.org.za/
In my own neck of the woods, there’s an OSM group with frequent meetups to guide newbies through editing. I think the best way for interested people to get involved is by learning in the company of experienced mappers, not just all by themselves at home. If such a stringent perspective scares some people away, at least the contributions of those who do stick around will be much higher-quality.
There really aren't. OSM is very freeform, almost anarchistic, compared to Wikipedia; very few edits are reverted and very few editors are banned.
I'd say there are probably five rules:
1. Don't copy from other maps
2. Edits should be 'verifiable' and 'on the ground' - i.e. no subjective information
3. Be liberal in what you add, conservative in what you delete - someone else is interested in it even if you're not
4. There's a special process for imports and automated edits
5. Be prepared to engage with other contributors
There are well mapped areas where just barging in and changing things will cause some issues, but for most of the planet the bar for improving things is quite low.