If you use access Gmail in Google Chrome on your computer, you can now view PDF attachments using Chrome's built-in viewer. The Chrome PDF plug-in is faster than the Google Docs previewer, its rendering accuracy is better, and you don't have to change settings anywhere for this to take effect. Just use Gmail in Google Chrome and the 'view' link will automatically open your file in the Chrome PDF viewer.
The change is also nice because Chrome's PDF plug-in actually lets you print, unlike the previewer which can only manage recursion printing (it generates a PDF of your PDF).
Users of Google Apps will receive the feature soon, according to a post on the Google Apps blog.