Do see any changes in how books are promoted in the future that you might incorporate into your website?
After I published my first book, I discovered through my own experimentation that one of the most cost effective ways to promote the book was through periodic price promotions - i.e. periodically offering my book for free or at a discounted price for a few days at a time. I then discovered that it was possible to greatly amplify the effect of these price promos by submitting details to a bunch of book promo sites.
But I was frustrated by the fact that most of these sites couldn't store my details from one promo to the next, forcing me to reenter all the info each time I ran a promo - which was every 3 months or so at the time.
I also thought it was a bit narrow-minded that almost all of these websites only catered for US readers - i.e. only provided pricing and links for amazon.com - thus ignoring readers in the other 12 countries (including the UK, where I live) where Amazon has local sites.
From a reader perspective, I also wanted an alternative to either receiving emails about all book promos, or none at all. And while some of the sites allowed me to broadly indicate the genres I was interested in, I still found this rather limited, leading me to ignore or unsubscribe from most of their mailing lists.
These combined with a bunch of other niggles (detailed here: http://www.readersintheknow.com/about), were the reasons I built Readers in the Know.
To answer your sub-question, I think book promotion has already got a lot harder and more competitive since I first published. Huge numbers of very poor quality Ebooks flood the market every month and this makes it both harder for good authors to rise above the noise, and for readers to sort the wheat from the chaff.
In some ways, this is similar to Google's challenge in helping people find the most relevant web pages to their search queries, and so the future of book marketing may need to adopt some of the same data search tricks and algorithms as Google.