Disclosure can occur anytime, even before your patent application is filed.  Beware, however, that almost all foreign countries have absolute novelty bars.  Any disclosure you make prior to filing your application will very likely foreclose all possibility of securing foreign patent rights.  The United States, Russia, and a few other countries have a one-year disclosure window, allowing a one-year period after initial disclosure before you need to file a patent application.

NDAs are a good idea, and can be useful in focusing the minds of the recipients on the fact that the inventor considers information regarding his new technology to be confidential.  On the other hand, NDAs are very difficult to enforce from a practical standpoint, and in a great many cases are essentially worthless.  It is possible to have recipients sign a non-disclosure, non-competition agreement, which can be easier to enforce, but most recipients are loathe to sign such agreements.

Keeping a notebook is a very good idea, provided the notebook is bound, with sequentially numbered pages, is signed periodically by a witness who understands the technology, and is kept in a safe place.  But the very best proof of inventorship is to file a patent application.  The application will almost always contain much broader conceptions of the invention than the notebook, and will hopefully include sufficient examples or other information to enable the invention.  Notebooks are very often lacking in those areas.

No, that is a terrible way of establishing an invention date.  The best way to draw your line in the sand is to file a provisional application.  With a filing fee of only $100, there is no excuse for doing anything else.

Disclosures to friends and family are usually not problematic with respect to bar dates because they are not public and they are done under an expectation of confidentiality.  On the other hand, the less disclosure the better, at least until a patent application is filed on the invention.  It is not at all uncommon that someone will accidentally either reveal something that was told to them in confidence, or will say something that somehow triggers a third person to invent the technology themselves.

The best protection, and to some extent the only reliable protection, is to get your patent application on file.

The USPTO publishes patent applications at about 18 months from the filing date of the earliest claimed provisional or other priority application.   But note that provisionals could be published earlier if they are combined in a utility filing.  For example, if an inventor files a first provisional on January 1, 2006, a second provisional on November 1, 2006, and a utility claiming priority to that provsional on December 1, 2006, both provisionals and the utility will be available on the USPTO website when the utility publishes at the end of June 2007.

Many foreign governments and the PCT also publish patent applications at about 18 months.  Thus, where there is a corresponding foreign or international application, the subject matter will be disclosed even if the USPTO fails to publish it.

The USPTO keeps provisional applications confidential.  Without authorization, no one can review the application, or even get confirmation that it exists.

On the other hand, once we file a utility application that claims priority to the provisional, the provisional will become part of the file wrapper of the utility and will be available on-line when the utility is published.  Publication occurs about 18 months after the filing of the provisional.