i have to agree with alex and dana. it's been awhile since i've seen this post but i've found that different days and different books need different tactics.
sometimes i preview for 10 minutes and frankly i don't even need to pr the book. other times i jump in and pr the book.
and i agree with you alex about the purpose. it really does make a huge difference when you read for a reason instead of just sort of picking up a book and reading without knowing why (although that can be fun too 
*hehe*)
