As of August 29, 2014, Google has decided to intentionally break old browsers. They say it's not a bug, it's by design here, even though Google's support page says it accepts Safari 4 as a fully supported browser.
If you want Google searches to go back to the modern style, you need to change your User-Agent string. For Safari, enable the Develop Window and use an option in there that works. Internet Explorer 9 (Windows) works, for example.
[crarko adds: I don't have an older system active at the moment to try this. It's inevitable that older software becomes obsolete, the same way older hardware does. I think the actual hint here is a reminder that if a site misbehaves, changing the user agent can be an effective troubleshooting tool.]
Mac OS X Hints