A very small but yet somewhat interesting observation has been made at Search Engine Watch Forums. You know how when you click on the "cache" link in the Google.com search results and Google will highlight the keywords you searched on, within the page copy?
For example a search on site:www.seroundtable.com danny sullivan brings back Reaction from the Search Community on Danny Sullivan's Departure post I did the other day. If you click on the cache link from Google.com, you will get to here and you will see that it highlights both Danny and Sullivan in yellow and light blue colors, respectively.
Now, if a result that is found within Google's supplemental results, and you click on the cache link, it will not show those keywords in highlights. An example, but there are many, is when you search on site:www.seroundtable.com TrackBack URL "Discussion on Google Indexing Itself?", the Google cache for that page should highlight the words "Google Indexing Itself" but it doesn't.
I have looked at several other examples, all tend to follow the rule. If your pages are in the supplemental results, and you click on the cache link from Google.com, it will not highlight the query terms you entered into Google.
Forum discussion at Search Engine Watch Forums.