Don't take the trouble, we won't commit it anyway. I fail too see the 
deficiency  and huge difference between adding contacts and adding 
contacts. But I can already hear the users being confused by one more 
addressbook preference. Two are enough.

Would you care to contribute those 5 simple lines of code, then?

Currently the add_source pref in IMP is used for both auto-adding from 
composed messages and for slamming to addressbook by manually clicking 
the add address in the message view. These capabilities are vastly 
different though, and really ought to have unique addressbook sources 
assoicated with them. With about five lines of code it would be simple 
to change this such that the save_recipients => { value = 
"addressbook_source" } (instead of just 1 or 0 ). This would then make 
the add_source config pref mainly for slamming to addressbook and (if 
desired) as a fallback incase save_recipients => { value =1 } (is is 
the default now). This simple change requires only 5 lines of code, 
but fixes a pretty big deficiency in the integration of imp/turba.