Not that this contributes much to the conversation but: YES on both counts.
I use GitHub's issue tracker in volume both for some fairly large projects (getcloak.com, walkscore.com, and wherebe.us) I've found that the Issues web interface leaves a lot to be desired. It's a fine v1 [v2 technically], but somewhat painful in practice once you have more than a handful of issues. The 280 North issues app was interesting but hasn't kept up with the latest GitHub features.
There are already plenty of okay Git GUI clients out there to manage your repository locally, but what I miss is the ability to edit (and preview!) the wiki locally. You can sync the contents via git, but then you are left with editing the raw source files directly.
Edit: Also would love to see this integrated with notifications so I can get Growl popups.