It can be really tough to separate the Google "dance" from "bounce" from daily fluctuations. The "Google dance" was originally a reference to monthly algorithm/data updates - that actual phenomenon has been gone for years now. Data is updated all the time, and the algorithm can change daily at this point. If you suspect an algorithm change has impacted your site (for example - a Panda update), you typically have to look at the dates of the updates and how the factors in that update are represented on your site. We keep an ongoing history here:
http://www.seomoz.org/google-algorithm-change
When I think of "bounce", I tend to think of sites that are moving up and down a lot for a sustained period of time (while other sites in the same rankings don't move). That can, in some cases, be a sign of an impending penalty or Google re-evaluating something about your site (your indexed pages, links, etc.).
Unfortunately, it can be really tough to separate "bounce" from daily fluctuations. I'm working on a project to track daily changes in rankings, and one thing I can tell you is that Google is far from stable. The average change in any given Top 10 day-to-day is surprisingly high. Anecdotally, the changes in deeper pages of the SERPs (2, 3, etc.) are even larger.
So, this could be perfectly normal. I'd keep an eye on a few things:
(1) Are you tracking using a 3rd-party tool, with personalization, localization, etc. off? It's really easy to see different SERPs these days, just by changing computers, being logged in, etc.
(2) Are you bouncing up and down daily, or is it a gradual change?
(3) Are other people in the Top 20 bouncing as well?
(4) Is this bounce having any real impact? This gets into @stubby's reply - if the bounce isn't impacting search traffic, the number of keywords you get traffic from, the pages that get traffic, etc., it may not be worth worrying about. Dig into Google Webmaster Tools and your analytics and find out what impact these ranking changes are really having on visitors to your site.