No matter what you personally think about the risk you are willing to take against challenges to fair use or your Section 108 implementation, it is important to also consider what level of risk the institution is willing to support.
Some publishers, for instance, are uncomfortable with any assertion of fair use rights, as they wish to avoid lawsuits at all cost.
Many libraries, however, are less risk averse, in part because of the generous provisions of Section 108 of the Copyright Act and the fact that there is very little litigation about these sections of the Act, and because librarians, in particular, are protected from statutory damages in fair use cases if their fair use assessment was reasonable and made in good faith.
For instance, Section 504(c) of the Copyright Act provides: "The court shall remit statutory damages in any case where an infringer believed and had reasonable grounds for believing that his or her use of the copyrighted work was a fair use under section 107, if the infringer was: (i) an employee or agent of a nonprofit educational institution, library, or archives acting within the scope of his or her employment who, or such institution, library, or archives itself, which infringed by reproducing the work in copies...." Note that in order to document this type of good faith practice, librarians should not engage in large scale digitization of in-copyright materials without engaging in careful Section 108 and fair use analysis item-per-item.
Not to mention the fact that state institutions may also claim sovereign immunity from suit (in other words, the best case scenario for an entity suing a public library for a fair use or Section 108 violation would be to obtain an injunction in many cases).
Nonetheless, it is important to understand the level of risk your institution is willing to bear and keep that in mind when conducting a risk assessment.
Low Risk Activities
Digitizing for Preservation under Section 108
Digitizing for Inter-Library Loan under Section 108
Digitizing public domain materials
Providing only thumbnail images of works in copyright with a fair use analysis
Digitizing materials with permission of the copyright owner*
*Note that copyright owner and the owner of the physical work may be different
Higher Risk Activities
Digitizing international materials
Digitizing orphan works (where the copyright owner is unknown/cannot be located)
Digitizing unpublished materials which may have longer copyright term lengths
Digitizing the above materials with open web access to the general public
Digitizing work created by someone famous or photographs of someone famous (other legal rights may be implicated)