There is a download of "Use The Index, Luke"—finally.
However, it got its own name to attract a wider audience. That's SQL Performance Explained.
It's a DRM free ePUB download.
It is, however, not possible to update the ePUB in the same frequency as the Web-Edition. It's therefore released in two parts. "Volume 1—Basic Indexing" was just put online and includes the first two Chapters—that is, everything which is online as of today. "Volume 2—Advanced Indexing" will be released after the rest of the book has been published on the web. That's probably 2012.
It's your chance to catch up if you missed the beginning. Just download to your e-book reader or smartphone and read wherever you like. The FAQ has some hints how to do it.
PS.: Yes, it's really the same as "Use The Index, Luke". Just another name.