Where I write about what suits me...
I slog through, because I believe in giving the book and the author the benefit of the doubt. Also, I just don't think that DNF (did not finish) books should be reviewed if you don't know the full content. :/
I feel obligated to finish unless it's just miserable and I've only had that happen once or twice.
It depends on the requirements of the "person/company" that sent me the book. Some require you read the entire thing for your review. But for most, I give it about 100 pages (in an average 250-400 page book) and then stop and I'm honest in my review why I could not press on. Seriously too many books too little time. - Margaretwww.CreativeMadnessMama.com
I usually feel obligated to slog through. I feel if I've signed up for something I should finish the book. If its for an author, usually I will write an honest review, send it on to them and ask them if they want me to post or not.