http://www.flickr.com/photos/little_pooky/10578881796/ All versions of Dragon NaturallySpeaking use the same voice recognition engine. Here is the demonstration that I created to show a friend using Dragon Medical 2 (most expensive) edition. You have to speak quite clearly, but it does work, even with an "accent." But basically all of them are the same. To see what each version can, and cannot do, see http://www.nuance.com/ucmprod/groups/dragon/@web-enus/documents/collateral/nc_025214.pdf
Yes, but if your work requires heavy formatting, it's best to dictate raw text and clean it up afterwards. The time it takes to train may vary. I bought the product a few weeks ago and am still working at it, but I haven't used it every day.
If you are a fast typist, typing is always going to be faster, but sometimes it's nice to take a break and read, especially if you need to reproduce large amounts of text that aren't in electronic form or easily OCR-able.
I am also a writer (of fantasy novels). Yes, you can easily dictate a book with this software. It has learned all of my made-up names and places. My editor has certainly enjoyed at my "ate and eight" and "their and there" mistakes. It has trouble with homonyms, but easily understands my fictional names and places. You may find it's an adjustment to say punctuation aloud while dictating, but you'll get used to it. Sometimes I slip and find myself saying "period" after a sentence in everyday conversation.
Without knowing if your book will include technical/professional language or foreign words... The most I can suggest is that it can reduce your need to type and help to force you to think in complete sentences.