In the new google chrome 6 stable beta, in built google chrome pdf viewer plugin is disabled by default as it seems to be buggy.
Here is how you can enable this feature
1. Go to google chrome address bar and type chrome://plugins/ in the address bar and clicking "Enable" next to "Chrome PDF Viewer" as shown in the image below.
2. As shown in the image above, click Enable link to activate the chrome built in pdf viewer. This will help you open pdf documents more easily and quickly but might be buggy some times.