Harry Potter and the Half-Blood Prince (spoilers)

I finished reading Harry Potter and the Half-Blood Prince last night. I enjoyed it.

Here's my questions and speculations from the book (warning: spoilers):


1) Why did Voldemort give Harry's mother the chance to live? I've had this question since book 1. My friend thinks he wanted her on his side, but did he really think she would join him after killing her husband and son? But then again, he never really understood love and thought death was the worst fate, so maybe he was that dumb.

2) Who was RAB? I was wondering about Sirius brother. His name started with an 'R' and we know the Dark Lord killed him, although I don't remember why.

3) Are there any of horecruxs left? We know of at least 2 in existence, the snake and Voldemort himself, but has the mysterious RAB managed to find and destroy the other ones like he did the locket? Or did RAB think Voldemort only had 1.

4) Is Snape really evil? He did kill Dumbledore, which would imply he is, but then, maybe it was necessary from some greater plot from Dumbledore. Dumbledore always trusted Snape, but then D. also said since he was clever, his mistakes tended to be larger. Also, by killing Dumbledore, Snape fulfilled his vow and probably usurped the Malfoy's place of favor (must have been rather pleasant for half blood to beat out the old wizarding families).

5) Does Malfoy have some redeeming qualities? At the end of the book, he was unable to commit the murder he planned. He also seemed to realize the cost of joining with Voldemort: failure is fatal to you and your family, and power is not all it is cracked up to be. I wonder if he realizes the stories his parents probably told him of the golden days with Voldemort aren't quite as rosy as they seemed now that he is back.