What is an update? Google updates its index data, including backlinks and PageRank, continually and continuously. We only export new backlinks, PageRank, or directory data every three months or so though. (We started doing that last year when too many SEOs were suffering from “B.O.”, short for backlink obsession.) When new backlinks/PageRank appear, we’ve already factored that into our rankings quite a while ago. So new backlinks/PageRank are fun to see, but it’s not an update; it’s just already-factored-in data being exported visibly for the first time in a while.
Google also crawls and updates its index every day, so different or more index data usually isn’t an update either. The term “everflux” is often used to describe the constant state of low-level changes as we crawl the web and rankings consequently change to a minor degree. That’s normal, and that’s not an update.
Usually, what registers with an update to the webmaster community is when we update an algorithm (or its data), change our scoring algorithms, or switch over to a new piece of infrastructure.