In the really light stuff it can be a good idea to use the top hole on the jib, as long as you are trapping out too much (I change holes between races if needed).
In average breeze and above we usually have the jib car further out than the 2nd post though.
The trim guides are useful but only as a guide, I noticed when our sails got older we needed more diamond and cunningham..
In light air as crew I find it useful to sheet the main, that way the helm can focus on steering.

Gill: Are you coming to our F18 Nationals? Should be a good event: http://www.deltalloydodc.org/