The new Google AdWords system allowing advertisers to target terms that previously might have been disabled, along with new minimum bids and a "quality score"-based ranking system, is now available to all advertisers.
What are the AdWords keyword status changes? is a FAQ from Google about the changes and the two new status types -- "active" and "inactive" -- that replace "normal," "in trial," "on hold" and "disabled." What is the AdWords keyword status column? from Google explains more specifically about the new keyword status. Keyword Evaluation Flow has pretty pictures to explain more how an ad gets moved into active or inactive modes.
The Google AdWords Performance Monitor explains more about the new quality score that is being used to rank ads. Previously, "AdRank" was calculated by the cost per click times clickthrough rate (CPCxCTR). Now it's CPCxQS, with QS being the quality score.
That quality score involves clickthrough rate, what Google perceives as the relevance of your ad text, a historical performance of the particular keyword and other factors. Despite the page, there's still not a lot of clarity about quality scores, but Google does try to give you a few tips on how to raise it.
Our past SearchDay article, Google Simplifies & Loosens Requirements for AdWords, has more information about the changes. Want to discuss? Visit our forum thread, AdWords Smart Keyword Evaluation Is Live. You might also check out Strategies for taking advantage of new AdWords system at WebmasterWorld, where discussion is on how to react to the changes.