The ads will appear just like other Facebook ads, but the users will be able to "Become a Fan" (if the ad is for a Page) or "RSVP" (if the ad is for an Event) directly from the ad, which will create a story in their profile page. Furthermore, these ads also contain friend actions, which means that users will be able to see which friends are fans of the Page or attending the Event in question.
From the user perspective, I like the direction Facebook is taking advertising. They're trying to make ads more like other content on the site, which should in turn make them more meaningful to users. However, instead of masquerading the ads as something else, they're giving advertisers the tools to blend advertising in with other content, but they never let them be too invasive. We'll see how it works for Facebook, which still has to prove it's capable of being a profitable company, in the long run.
Additional Facebook Resources for Brands