All the new Kindle Fire models will come with adverts. Every time you wake the KF from sleep you'll see an ad on the unlock screen. According to the press release:
Examples of special money-saving offers that customers will enjoy include a $5 credit in the Amazon MP3 Store and a $5 credit for select titles in the Amazon Instant Video Store. Customers will also receive special offers and screensavers from brands like AT&T, Discover and Intel, such as a special offer of a $10 Amazon.com Gift Card when a customer uses their Discover card to purchase a digital product on Amazon.
What's more, according to the product page for the Kindle Fire HD there will also be ads on the lower left hand corner of the home screen. So the entire time you use this tablet you will be bombarded with ads.
It's often been said that the Kindle Fire is Amazon's digital storefront; apparently Amazon decided to take that literally and put up signs advertising sales. I don't know about you, but I hate ads enough that this might be enough to turn me away from the new Kindle Fires. I'm one of those people who actually paid Amazon to remove ads from my Kindle, just so I didn't have to see them.
But in this case I'm not sure it's such a big deal. You can always replace the home screen (I do actually like the stock Android home screens) and editing the lock screens is also a relatively simple task. So really anyone who wants to get rid of the ads can do so; it just takes a little work.