Google Stat:

When looking for new keywords, remember that long tail can some times be too long. Compared to shorter keywords (those with two to four words), keywords that contain five words or more drive less than half the volume of clicks and impressions on average. It’s a similar story for keyword character length — keywords with 30 or more characters (including spaces) also drive fewer than half the clicks and impressions on average than shorter keywords. Longer keywords take more effort to define and deliver less than half the volume, so spending time on them may not be in your best interest.

Did you know that Ad Extensions can lead to improved conversion and a higher Quality Score?

Ad Extensions make your PPC ads stand out and they also offer users more options, so it’s no surprise that they increase CTRs and interaction with ads. Some examples of extensions are click to call phone numbers in mobile ads, sitelink extensions and offer extensions, which give users printable coupon for offline use. Studies show that things that don’t match stand out to people (like a sweater and a bathing suit, or so my friends keep telling me) so if you’re using Ad Extensions, your ads are more likely to be noticed and clicked on.

Extensions don’t cost anything extra*, and since they traditionally do increase CTRs, it’s possible that Google automatically bumps up your Quality Score when you use them. Google plays it pretty close to the vest about how scores are calculated, so this is speculation based on what they have admitted. However, even if they don’t automatically factor in the use of Ad Extensions, extensions do improve CTR, which means you’re likely to get the score boost either way. 

There are no additional charges for extensions right now, but you’ll still pay for a click if someone uses the click to call feature or clicks on a sitelink instead of the main ad.