<Disclaimer>This is personal notes of what I retained during the session. This can be incomplete, partially right or wrong. It is just  part of the notes I took and what retained my attention. Nothing prevents the user to get more information on their favorite web site.</Disclaimer>

This presentation, held by Bjorn Erik Olsrod from FAST, starts by explaining that the FAST ESP Web Part, able to interact with the FAST Search engine, is available for free on CodePlex and start with a first demo showing how to use it.
How this works is pretty simple. The browser sends the request to SharePoint which will query the FAST ESP. In return, the engine sends the result in XML back to the FAST ESP WebPart in XML. This XML is finally transformed to HTML using an XSLT and displayed to the user. If the user wants to change the way the results are displayed, s/he can modify the XSLT and Bjorn shows how to do it and displaying the thumbnails of the documents. He also integrates a Silverlight control showing the images documents.
In some situations, some logic might be necessary to display the result. The problem with the XSLT transformation, as it runs on the server, is that it cannot know the client context. To solve this problem, the XSLT is modified to transform the XML received from the FAST ESP to an XML encapsulated inside the HTML. Then, the final HTML displayed to the user is transformed by a Javascript. The demo showed at this time was able to adapt the amount of information displayed to the user based on the size of the browser window.
An even complex scenario is to implement a “search as you type” scenario. To do that, it is possible to implement a page stored in a SharePoint document library that will act as a web service. This service will receive the AJAX calls from the browser and will send back the result to the browser.