by Damyon Wiese.
What is are describing sounds similar to the repository code for 3.3. Look at repository/googledocs as an example.
There are 2 cases with when accessing a service with OAuth:
1. You want to access on behalf of the logged in user
2. You want to access on behalf of some kind of system user with magic privileges (without giving those privileges to the logged in user).
Case 2 is what we use the "system account" for. Again - see the examples in that repository/googledocs which mixes both kinds of access.