The author of Neighbors describes a horrifically brutal massacre of the 1,500 Jewish Poles in the small town of Jedwabne, Poland shortly after Nazi Germany's invasion of Eastern Poland; many were stabbed, decapitated, drowned, and mutilated before the remaining Jews were burned alive in a large barn. The author also argues that half of the town's male Polish-gentile actively and readily perpetrated the massacre (including the town's mayor and council). The author also argues that the Germans largely did not participate beyond taking photographs, and encouraging the Polish gentiles population with their mere presence.
How accurate are the testimonies presented in this book, and do the events at Jedwabne reflect a broader sentiment in Eastern Poland - that given the chance, many Poles (and other Europeans) would commit (and have committed) similar atrocities to their Jewish neighbors?
Yes, this is a true story and the author is a respected historian. Poland and other Eastern European countries have a sad history of violent anti-semitism. Particularly poignant are the killings of Jewish survivors of the Holocaust after the liberation of Poland: between 1944 and 1946 hundreds of survivors were killed by Polish gentiles. The largest mass killing took place in Kielce in July 1946 when 42 Jews were killed. See this for further reading.
Also poignant are the numbers of Jews in hiding during the war that were betrayed to the Germans or killed by Polish gentiles. Particularly harrowing are the stories of escapees of the mass escapes from the death camps of Sobibor and Treblinka being killed by Polish partisans and peasants when they were hiding in the forests around the camps.
However, mass killings on the scale of Jedwabne were rare in Poland. They were, however, not so rare in the Baltic states, particularly in Lithuania where the Germans found very willing executioners among the local gentiles, whether spontaneously or as part of their duties as auxiliaries to the German forces. It has been argued that the majority of Jews killed in Lithuania during the war were killed by Lithuanians and not by German forces. See this for further reading. Similar things happened in Estonia in Latvia though not on the same scale.
A serious question I have is whether it is true that amazingly some German soldiers (not SS) tried to prevent the pogrom, it was so brutal. This is not impossible -- I have also heard that the regular army sometimes tried to intervene between Jewish civilians and the SS (and sometimes willingly helped the SS) but I can find no source online which discusses the role of the German army in Jedwabne either helping/trying to prevent/doing nothing during the massacre.