Stability verification amidst rapid releases
I must say, that it's pretty strange to see rational discussion of software testing - it's a part of the industry that's long been overlooked.
Rapid release cycles can deliver stable builds. The process is inherently difficult, but it can be done with extensive communication between the development and the testing groups.
First, the development team must meticulously maintain a change log, and before the release, communicate these changes to the test team.
The test team can then either determine with white-box methods which areas to test, or obtain the information from a less-partial developer.
This allows the test team to proceed with focused testing on areas that have been changed, in addition to the broad and shallow 'smoke-test' that is applied to the entire product before general release.
This strategy is entirely dependent, of course, on sound design and testing principles as Frank outlined earlier.