I've previously reported about Gmail's experiments with image ads and personalized ads, but it seems that these tests are two pieces from a puzzle: a new ad-matching system for Gmail.
New York Times reports that the new algorithms try to find better ads. "Alex Gawley, Google's senior product manager overseeing Gmail, (...) said Gmail's revamped ad-matching system, now in limited tests, analyzes context as well as the content of an individual message. It looks at what he calls 'signals in your inbox,' like whether you open messages with particular keywords and don't open those with other keywords."
Gmail will also include static image ads. "For example, an e-mailed offer for a ski package showing a skier on the slopes could be accompanied by an ad on the right side of the screen, showing a competing offer, replete with another skier coming down another slope. Mr. Gawley said the image used in the ad would be static, not animated, and would be used only in cases where the e-mail message itself showed images."
Gmail's new ads will still be related to your messages, but Google will add other signals that will make the ads an extension of your inbox. Just like Google shows small images ads next to images search results and uses your preferences to personalize ads, Gmail's contextual ads will improve using more data.
As long as the ads are relevant, moderately useful and they aren't distracting, Google is still on the right track. It might take a while to get used to the image ads, but the ad displayed below the messages and the list of messages will be the most obnoxious. "Gmail presents a single text ad when you look at an inbox view and haven't selected a particular message," according to the New York Times.