You might not notice a big impact on your search results early on, but they should steadily improve over time as you use Web History. (slaw.ca)
Set your browser to delete cookies and web history when you close it. (slaw.ca)
If you're signed in to your Google Account and have Web History enabled, you might have noticed the drop down list of suggestions from the search box as soon as you start typing, it's Google Suggest. (betaout.com)