One of the primary reasons it takes at least three months to ramp up on a project is simply due to communication. The vast majority of the meta information about the project lives in the heads of the developers. Even if they have all the code cleanly laid out, in one repository, with lots of comments, it will still be hard to sync mentally.
- Why was X done instead of Y
- Where are we going
- Where did we come from
- What are the standards
Anything beyond a trivial code base has these issues. Since it only lives in the devs heads, it takes time for them to remember, and then to tell you. So you accumulate bits until all is clear.
Castle on the River Wraith 