I tested SerpBook for aprox. 45 days and finally gave up on it. SerpBook is a great idea: We wanted something for lower-rung clients to track their improvements (i.e. the viewkey), but Yahoo! and Bing were virtually never tracked correctly, and there were often dramatic Google discrepancies, as well. As Gyuman noted, one can track the same keys and URLs, either in different or even the same one category, and experience Google ranking discrepancies by as much as 200 and 300 places. This is not a data center issue: There is no one data center for any given Google service region that ranks a URL/keyword #1 in one data center and does not rank it at all in another. SerpBook also does not automatically list the highest ranking URL on a site for a given keyword, which I found odd.
Lanbo was relatively defensive in initial contacts with him about this stuff, in one instance bolding and italicizing "you set it up that way" when doing my best to explain to him that I had not, and that I did indeed understand the "exact URL" feature, etc. Later, I was notified that he had discovered and fixed some bugs - he was notably more mellow in these correspondences. Nonetheless, the problems were never really fixed. I cancelled.
I should note that we use several tools, all of which concur with one another almost exactly: LinkAssistant's "Rank Tracker", MicroSite Masters and one other, the name of which escapes me at the moment (I don't ever use that one myself, just receive reports).
Being fair, it is entirely possible to rank #1 in one data center and #2 or #3 (etc.) in another. Its occasionally possible for these variations to be more pronounced, but not by 50, 100, 200, 300 spots.
