Google added a new contact chooser to Gmail that present you a list of contacts to include in your email, that eliminate the need of relying on auto-complete for addign recipients. Click the "To:" link (or Cc:/Bcc:) when composing a message and you'll see a box like in the image; clicking contacts will add or search for others. If you use contact groups, your groups’ll appear in a drop-down menu in the contact chooser, so you can select contacts from the groups you've already created. And if you happen to use Gmail in Chinese, Japanese or Korean, being able to pick from your list of contacts should be particularly useful since auto-complete doesn't offer the same search as you type experience that it does in other languages.