I have created 3 groups for adcenter and and i got impression for 1 groups keywords only other two group(each group have 50 keyword and keyword selection is proper) dont have even single impression. all keywords are active.
adcenter can take a day it seems to really get actice - and reporting can be slow. If you still have issues give them a call - they offer free keyword analysis and optimization. In fact they will probably call you if the performance is low.