Designated Hero: Ricciardo (day 3, story 6) is a man who is in love with a married woman, and so, he takes advantage of her jealousy regarding her husband by impersonating her husband and having sex with her in the bathhouse. She doesn't even find out that the man she had sex with was not her husband until later. In other words, he rapes her! And Ricciardo is supposed to be the good guy!
(Day 5, story 1) ends with Cimon and Lysimachus getting married to the women they love, Iphigenia and Cassandra respectively. Yay! But they only do so after they have violently killed the men, Pasimondas and Ormisdas respectively, who were supposed to marry the girls in the first place, so whoop-dee-doo!
Also, (day 5, story 8). In it, Nastagio is in love with a woman who rejects him. So, as he walks along his way, he hears of a lady who rejected her knight suitor and rejoiced when he killed himself. She's sentenced to be hunted and killed by him, eaten by his dogs and brought back to life every Friday for the same amount of years than the months she was cruel to him. Nastagio uses this to frighten the woman he loves so much she finally agrees to marry him. In other words, he blackmails her into marrying him!
While this collection of tales is not exactly feminist, women are treated as much more willful and independent than those in other tales of the time.
While Jewish characters are rich and occasionally miserly, they are also said to be wise or even virtuous. The tale of Melchizedek the Jew (day 1, story 3) is remarkable for having an Aesop arguing that Judaism and Islam are just as valid as Christianity.
The work is subtitled Prencipe Galeotto (Prince Galehaut), the go-between of Lancelot and Guinevere, a reference to the many go-betweens in Decameron and also a reference made by Dante in Inferno V.
Boccaccio was actually a huge admirer of Dante and incorporates a number of references to Dante in the Decameron and elsewhere in his work; for instance, on the first day, the courtier-diplomat who serves as a hero of sorts for one of the stories is mentioned in the Comedy as being damned to Hell for being an unrepentant "sodomite" (whether this means "homosexual" or "pedophile/pederast" is unclear) despite being an otherwise honorable and upstanding gentleman.
Older Than They Think: Most of the stories come from sources way older than the book; Boccaccio just brought them to his time.