I have noticed my adwords control panel tell me my ads will not be shown for a particular keyword or phrase due to my bid being too low; usually by several dollars. Further I have noticed when I do not raise my bid I end up with several impression for that phrase despite what the control panel has indicated and often times my ads are being shown at position 3. Moral: Don't be so quick to raise your bid for a keyword just because your adwords control panel says to. Wait and see what action you get first.