Dan Cohen's American Historical Association conference talk "Is Google Good for History?" is an absolute must-read (as are the comments that follow). It's the most even-handed examination of the complex issues I've read, and he touches on just about every single one of the major points that should concern users of Google Books. You should read the whole thing, but I really liked this particular paragraph:
"We should remember that the reason we are in a settlement now is that Google didn’t have enough chutzpah to take the higher, tougher road—a direct challenge in the courts, the court of public opinion, or the Congress to the intellectual property regime that governs many books and makes them difficult to bring online, even though their authors and publishers are long gone. While Google regularly uses its power to alter markets radically, it has been uncharacteristically meek in attacking head-on this intellectual property tower and its powerful corporate defenders. Had Google taken a stronger stance, historians would have likely been fully behind their efforts, since we too face the annoyances that unbalanced copyright law places on our pedagogical and scholarly use of textual, visual, audio, and video evidence."
Also, HNN has posted video of some of the panels, including Cohen's talk, Paul Duguid at the same event, and the "What Becomes of Print in the Digital Age?" panel, featuring James Cortada, Anthony Grafton, and Abby Rumsey.