Clare Dudman, on her blog Keeper of the Snails, writes about the ways in which the internet can enhance the experience of reading a book. In addition to her list, there is an interesting group of suggestions in the comments discussion, as well as a debate about whether the pleasure of reading is best limited to the book itself, rather than including secondary activities such as looking up the location of the setting on Google maps.
For me, the main way in which the internet enhances the reading experienceis to use the plethora of online book reviews. If I am deciding whether or not to read a book, I might search for the title/author and then skim reviews on blogs or other websites (eg newspapers) - but not read them very thoroughly as I don't want to know too many details or opinions at that stage. After I have read the book, however, I very much enjoy reading other people's review of the book to see other perspectives on it - and, if there are online comments for the review I'm reading, I like reading those and perhaps joining in the discussion.
Our Friend Feed crime and mystery group (which anyone is welcome to join - if you are quick you can be the 100th subscriber as we reached 99 this morning) is an extension of this process. Links to reviews of books are posted, either automatically or manually. The stimulating book-focused discussions that develop, either at Friend Feed or at the linked article, can either persuade me to read the book (or not to read it!), or bring out aspects of it that had not previously occurred to me.
The internet is so good at enabling one to discover books and to read them, either by visiting good book websites (my favourite is Euro Crime as I am becoming increasingly taken with translated fiction) or by general searches. Buying the chosen book online is also a huge advantage on the old days (pre-Internet) of traipsing round bookstores and not finding a desired title in stock (but being tempted into buying other books in the process, of course). Although Amazon does feature "customer reviews" of books, I don't usually find these as useful or engaging as the reviews I read on blogs (particularly the blogs I regularly visit) or via an internet search, which identifies newspaper or magazine reviews as well as reviews on blogs I didn't previously know about. So I tend to use Amazon (or other bookselling site) mainly for the purchasing function and not for the reviewing/recommending option.