I was able to successfully connect to the Intuit Partner Platform for the QuickBooks API using this module.
Here is a link to my Oauth Connector Settings (hopefully that will at least help someone get started): https://gist.github.com/camikazegreen/6491477

It doesn't quite work as expected though, because the User ID Resource returns an XML file that looks like this: 

<?xml version="1.0" encoding="utf-8"?>
<UserResponse xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://platform.intuit.com/api/v1">
  <ErrorCode>0</ErrorCode>
  <ServerTime>2013-09-08T23:52:49.2134626Z</ServerTime>
  <User Id="56730036.jv9j">
    <FirstName>Cameron</FirstName>
    <LastName>Green</LastName>
    <EmailAddress>example@gmail.com</EmailAddress>
    <ScreenName>example@gmail.com</ScreenName>
    <IsVerified>true</IsVerified>
  </User>
</UserResponse>

I can set the "Field" to User and it will associate it to the user, but it will not parse. It returns the whole User array instead of just the value for the email address. EmailAddress, doesn't return anything. I tried xpath, querypath, etc. with no results.

I still need to figure out a way to pull the Company Realm id out of the URL parameters during authentication and save it to the database for future use before I will be able to make any API calls. The URL looks like this:
Request URL:http://qboa.loc/oauth/authorized?oauth_token=87345c37592375n923479yksjhi...

I was able to connect Twitter in like ten seconds, so good work on that one!