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Not sure how far back you can get QS info for, but I ran a keyword report for a few clients that were using adwords as far back as 2003 and the report seems to produce a QS score for the "All Time" date range. Normally you'll get an error message telling you that certain types of reports or data are only available for a certain (usually more recent) period of time. So I'm not exactly sure what to make of this info.
Will be useful to trend QS movements and shifts to better identify problem areas. Wonder if Google will aggregate campaign QS and place it as one of the metrics in the account snapshot area so that we can trend the overall QS at the campaign level at least like we can already do with other metrics like Impressions, Clicks, CTR, Conversions, etc.
Cool stuff - I like where this is going!