Google Instant is supposed to make searching faster, but you need a pretty good Internet connection, a modern browser and a decent computer. Google Instant is not available if you use IE6 or other outdated browsers and it's automatically disabled if you have a slow Internet connection.
Now Google also disables Instant if you have a slow computer. "If Instant gets automatically disabled, we continue to check your computer speed and will re-enable Instant if your performance improves," informs Google. If you don't like this change, you can disable it from the search preferences page. Just select "always show Instant results" in the "Google Instant predictions" section.
I've tested this feature on an old laptop and Google's implementation isn't great. Google Instant continues to be enabled for the initial query even if it's slow, then it's suddenly disabled when you visit Google Search again. Google doesn't show a message next to the search box to explain why Instant is disabled and not many people will visit the search preferences page, which both an explanation and a fix.
This is just one of the 17 updates from last month that improved Google Search.