We all should know by that Google makes around 400 changes a year to its search algorithm (yes, that is over 1 change a day), with some such as the recent 'freshness' update being more significant than others.
However last month Google made a change to its AdWords algorithm which is significant in several regards
1. This affects Google's revenue if they get it wrong
2. This affects advertisers (e.g. those with fixed PPC budgets may find they get more or less for their money now)
What actually changed was an update to the 'Quality Score' factor that is given to each advert within Google's pay-per-click system. Quality Score in the past has previously been an arbitrary weighting that was given and that meant more experienced online marketers could mysteriously bid less than their competitors and still get a higher ranking in the search engine results pages (SERP's).
More and more is now gradually known about Quality Score (mainly thanks to Google posting blogs and videos on the subject) and it is now widely accepted that it is a mixture of three things:
a) the historical performance of the advert (what percentage of people actually clicked on it)
b) the relevance of the ad text to the search term (e.g. are you actually advertising for what people are seaching for)
c) the quality of the landing page (how relevant is the page you're actually taking users to?)
Google has now put a greater emphasis on the landing page quality, which to me makea a lot of sense. All too often you get taken from a PPC advert through to a page that has very little to do with the craftily-worded advert.
I just hope they also factor the page speed performance into account as well!