I am, or was, a significant mapping contributor for OSM in the UK. Before I stopped editing in April, I was UK #1 contributor (last person to touch most db objects). At time of writing in June 2011, I have fallen back to #3 in the UK. Globally, I am #150 for number of ways contributed. I also organised several mapping parties and attended a few run by others. I became involved in OSM because I support the free exchange of information and fear we are moving into what Lawrence Lessig calls a "permission based society", where decisions are concentrated into the hands of publishers. Therefore, I support OSM's goals but not necessarily "OSM the institution". For whatever reason, I never became involved in OSMF organised events, such as SOTM.
For a variety of reasons, I am ceasing to be a regular mapping contributor in OSM, but I may be involved in activities that support a wider range open data projects.
Why I am No Longer Mapping in OSM
Strategic control of OSM is not in the hands of map contributors. This was clear to me by the lack of direction in community forums and from my discussions with OSMF. The way decisions are taken and where responsibilities lay are very opaque. This moves decision making from the creators to the publishers of the data.
In my many discussions with OSMF and mailing lists, I found the process and results were unproductive. This was partly due to the reason above, but also due to the behaviour of participants. Instead of constructive and rational debate, discussions are dominated by dogmatists, demagoges and wishful thinkers. Criticism of current OSMF policy is often met with the accusation of being a troll. For an INTJ personality like me, this was frustrating. The favourite logical fallacies in OSM seem to be the perfect solution fallacy and ad hominem. This behavior extended to the highest level in the community. See also, Nietzsche's Gay Science, aphorism 2.
In the spirit of OSM of trying to fix problems, I did what I could. I am not particularly well adapted for this task. From what I could tell, this is no sign of significant change in the foreseeable future and normal participants lack the ability to enact change.
OSM Mappers are now faced with the unpleasant task of repairing the data, as non-relicensed users are filtered. This wastes a massive amount of time and energy.
There is little or no community support for OSMF making strategic decisions, it simply operates in a power vacuum. 
And the problems I listed in the previous section persist.
I am no longer a mapping contributor in OSM, but my data may arrive in OSM indirectly from forks.
I will continue my involvement in projects that can benifit the entire open data ecosystem (including OSM), so don't delete my dev or wiki account yet! From OSM's point of view, this is mainly old map scanning and some software development.
My past contributions will be PD/CC0 licensed, to enable reuse by OSM. This is mainly happening because of my loyalty to local mappers and certainly not to support the license change.
If OSM changes, anything is possible. Many people in the "magic circle" are strongly pro-PD, but seem to submit to the minority of ardent pro-SA people. The majority of mappers don't really care about this at all.
Thanks for All The Fish
A few groups in OSM deserve my thanks:
- The mapping contributors - the real generators of value in the project. They are "the creators", in Lessig's jargon.
- The sys admins - they never lost one of my edits, which is quite amazing.
- Mapping party and social organizers - a good laugh had there. We can probably continue in some way.
- Probably others who supported my role in ways I can't comprehend.
Hall of Shame
I'm not really going to write that! Remember, be constructive.
"This precept, however, give I unto thee, in parting, thou fool: Where one can no longer love, there should one - pass by!"
With regard to what is commonly meant by intemperate discussion, namely invective, sarcasm, personality, and the like, the denunciation of these weapons would deserve more sympathy if it were ever proposed to interdict them equally to both sides; but it is only desired to restrain the employment of them against the prevailing opinion: against the unprevailing they may not only be used without general disapproval, but will be likely to obtain for him who uses them the praise of honest zeal and righteous indignation. John Stuart Mill