I did this from home early this morning (probably at the same time that I messed up Daniel Vaughan's name in my Silverlight Cream post). By the time I got everything fired up here, the blog post I used had rolled off my blog roll, but I found it again here from Tom Mertens.
The implication is that you can get all 3 eBooks, but what I actually got was selected chapters of the ASP.NET Ajax book and the Silverlight book, but was able to download the LINQ book complete, and I figure that's great! If I had to pick one, it would be that. I have the Silverlight book, and I have a great ASP.NET AJAX book already.
The actual Microsoft site has a "Special Offers" section with not only the free eBook offer, but also information about a free clinic.
Free stuff is always good, particularly if it's useful!