Zivush - 4:43 pm on Oct 9, 2012 (gmt 0)
Two 'direct' metrics that are easy to asses by any Search Engine are:
1. SERP CTR (Click-Through Rate (CTR) from the SERPs themselves) can be seen in WMT.
2. Dwell time (how long it takes to return to a SERP after clicking on a result).