I was going through the adwords blog a few days ago.  It said that the loading time of a landing page will affect the quality score of a site.
Load time is the amount of time taken for a user to see the landing page after clicking on an ad.

The reasons stated for doing this are:

1.    Users have the best experience when they don’t have to wait a long time for landing pages to load. Interstitial pages, multiple redirects, excessively slow servers, and other things that can increase load times only keep users from getting what they want: information about your business.

2.    Users are more likely to abandon landing pages that load slowly, which can hurt your conversion rate.
Google says that this change should be made in the next couple of weeks. Load Time evaluations will be added to the Keyword Analysis Page after which there will be a one month notice period to review your site and make necessary adjustments.

After the notice period, the minimum bids for the sites will be adjusted. ie. Keywords with landing pages that load very slowly may get lower Quality Scores (and thus higher minimum bids). Conversely, keywords with landing pages that load very quickly may get higher Quality Scores and lower minimum bids.