What I found to be the REAL tragedy of this story was - that at 38 - Severus Snape died a virgin.
HEY! I got married at 38...
Speaking of Slughorn, my wife pointed out this: in HBP, Slughorn keeps saying that Harry seems to be a natural at potions, just like his mother was. Now that we know from book 7 that Lily was Severus' best friend at Hogwarts, perhaps she was such a "natural" at potions because she was getting help just like Harry was, from Severus (she directly, Harry from the HBP's potion book.)
Makes me wonder if Slughorn knew what was happening all along, and was secretly being sarcastic when he kept praising Harry...
Sigh. I so enjoyed having seven really long books to read without that kind of cr*p.