For some reason, Google's caching feature is more and more difficult to use. The "cached" link is hidden inside the Instant Preview box and it's no longer available in the mobile interface.
Now the keywords from cached pages aren't highlighted if you are logged in. Search pages use encrypted connections (HTTPS) when you're logged in and this disables referrals, so that's probably the reason why Google no longer includes the query in the cached pages URLs. Google suggests to sign out and you can also use a different browser or the private browsing mode, but there's another way to bring back keyword highlighting:
- click the "similar" link in the Instant Preview box instead of clicking "cached"
- replace "related" with "cache" in the URL and press Enter.
If there's no "similar" link, you can copy the query, go to the cached page and paste the query in the address bar between "+" and "&cd=".
There's also a cool Chrome extension called MultiHighlighter, but you need to copy the query, visit the page, press Ctrl+Shift+A and paste the query. If you use Internet Explorer, Google Toolbar has a cool highlighting feature.