Actually having a laptop has made me do some work on my game since I got back from holiday as I can now take it round my girlfriend's parents at the weekend and be set up to work.
Just a minor thing - I've changed the collision filtering system slightly so that the ID of the objects are embedded in their info along with their group. This means that objects like the buzzsaws that use invisible shapes to keep them in place can now avoid colliding with other buzzsaw's invisible shapes. Blah, blah. Not very interesting.
Funny story - spend about half an hour updating code all over the project to use MAKEWPARAM() to encode the collision group and the object ID into Box2D's existing shape filter then discovered that the filter is a 16 bit short. Doh! I've instead just used the CategoryBits field to store the object ID where required.
I'll hopefully have some more interesting updates soon but I'm still on holiday so I'm off for a beer.