Update: Emaderton3’s comment below includes this formula for converting the new impact score into the former priority score: [5 * (new impact score - 10)] + 100 = old priority score
e.g., [5 * (80 - 10)] + 100 = 450
An impact score of 80 at the 59th percentile means either the study section discussed all proposals, or someone took an interest in your otherwise triage-destined application and advocated for its discussion.
The new scoring range is from 10-90, with impact scores under 20 most likely to be funded … perhaps under 25 since ARRA has relieved the system of some of the backlog of potentially fundable applications. Percentiles issued in this round reflect only the current study section in which the application was reviewed (assuming the study section had 25 or more applications under review … if fewer than 25, then pooled with either all CSR or all IC applications, as appropriate to the review group’s affiliation).
You can find details on the scoring procedure and interpretation as well as reviewer guidelines by mechanism at the Enhancing Peer Review Website.