Which layer ideally controls the accuracy of the stack of GIS parcel layers?

The land survey or cadastral layer.  If this data is imprecise or inaccurate, every parcel built on top of it will be inaccurate as well.

Do "Open Source" databases and software foster collaboration? If so, how?

Yes, and for a very simple reason: "Open Source" databases are free and in 2010 extremely functional. Some products such as PostgreSQL have GIS-aware add-ons available such as PostGIS that can be used to spatially query the data. Alternatively, data can be prepared using commercial GIS systems and then shared to open source databases allowing a lot more stakeholders in an organization to simultaneously query, view, and comment on the data. Organizations tend to avoid large license agreements for software licenses that may only be used for a particular project.

Digging deeper into the WhiteStar Exploration Cube, what trends are you seeing nationwide in the oil patch?

There is a strong trend toward centralized data management for exploration using ArcGIS Server technology with SDE. Customers want to use data on a turnkey, nationwide basis limited only by their own creativity, not data availability.

What is the best practice for basic posted map generation?

You should be able to select (or expand) an area of interest, select the data layers for it (i.e. wellspots, city boundaries, land survey), download it in an appropriate format and upload it into your system in preparation for map plotting in at most 30 minutes for a five county area or smaller area.

Does technology play a role in increasing collaboration?

Yes, technologies such as WMS and GIS Map Servers provide a framework for multi disciplinary map and idea data integration.