Hi Jon,
I'm just about to head off on annual leave so a quick response from me.
Yes we would expect the topics to be different if people want them to be. At user group meetings we are very much driven by what the members want to know about.
Chris has offered to come and do a day on whatever we want him to talk about/facilitate, so really it's up to us to say 'we want to do this'.
Regarding giving back - this can be in many forms including but not limited to bug testing, bug squashing, updating/writing documentation, writing blogs about joomla! 3.0, getting involved in working groups, replying to posts on the Joomla! forums, learning how to help with other areas of the Joomla! project in accordance with your own skillset.
To be honest, any way that we can help the project!
Ruth