Marcia posted a thread at WebmasterWorld informing us that Yahoo! Search is now highlighting the keyword search you have done, when you click on the cache link.
For example, if you search on search engine roundtable in Yahoo! Search and then click on the cache link under the top result, you will notice that the keywords "search" "engine" and "roundtable" are all highlighted in the cache results. Here is a screen capture:
Did Yahoo! every highlight keywords before? I am not sure if they did or not. There is a WebmasterWorld thread from November 2004 saying the Yahoo! cache does not have highlighted keywords anymore...
I saw it for the first time yesterday evening. They're still not showing a cache date, but the words in the search term are now highlighted in bold, bright colors.
Forum discussion at WebmasterWorld.