Wow! There has been a lot of posts since I last checked this thread. I'll try to get in here with some comments on the different topics now
I believe our best choice for the future is the Qt Mobility Contacts API. The only problem is that the Qt Mobility library is still only in extras-devel, and thus cannot be moved up to extras testing. Our best choice for now is probably to either use your .vcf workaround or figuring out how to talk directly to the abook.
I think we should place it in ~/.config/mbarcode/temp/ since that is where the other config files are stored.
I think we should add a recommendation for the plugins as well (at least the "official" ones) and go for a enable/disable option in the settings. That is the reason why mbarcode depended on the plugins and not the other way around the begin with, but I think we can solve this with the "Recommended:" option in the control file. I'll check this out later (if noone beats me to it).
Isn't the 1D plugin deprecated? I believe it does nothing but to serve as an example plugin at the moment.