I'm sure you'll be pleased to know that I've now accepted the OSM Contributor Terms, following OSMF's endorsement of LWG's interpretation: http://docs.google.com/View?id=dd9g3qjp_126n2n4b4dt
I was initially unable to accept the new contributor terms because, as they are written, I believe they are incompatible with my use of OS OpenData for some of my previous edits.
The OS OpenData license clearly states that any sub-licenses must include an attribution requirement, and must also enforce a similar attribution requirement on any further downstream usage.
The new OSM Contributor Terms (in particular clauses 2 and 3 of version 1.2.4) require mappers to grant wide-ranging rights to OSMF for future and past contributions. In particular, these rights are sufficient to give OSMF the right to release contributions under a license that need not require any attribution (it need only be "free and open").
Because of the attribution requirements of OS OpenData, I am unable to grant the requested rights to OSMF. However, it has been suggested by LWG members that this is not the way they intended the CTs to be interpreted. (See eg http://lists.openstreetmap.org/pipermail/talk-gb/2011-June/011931.html )
Following a number of informal statements, LWG has finally agreed a formal statement concerning how the CTs should be interpreted: https://docs.google.com/View?id=dd9g3qjp_123cdchck62
This satisfies my concerns (though obviously in the long run the CTs need amending to correctly reflect this interpretation). However, the CTs are an agreement between myself and OSMF (rather than LWG), so I needed official confirmation from OSMF before I can agree to the terms under this interpretation. That eventually happened, and so I've now agreed to the CTs.