Quick-n-dirty comparison
We felt sure that the American philosopher and satirist Mark Twain - author of The Adventures of Huckleberry Finn - would be well represented, so did a quick search for 'Mark Twain letters'. Close to the top of the list, we found Volumes I and II of the complete collection - Mark Twain's Letters - published in 1917.

Foreword of Mark Twain's Letters in Live Search Books
(click for larger image - as seen on 1280x1024 screen)
These we were able to browse on line and also download in PDF format - the same was true of The Adventures of Huckleberry Finn. What we found annoying, though, is that our three key search words appeared highlighted in green on every page they occurred on line - something Microsoft needs to work around by offering a direct link to the book's source URL.
Also, the downloaded versions, in PDF format, are pretty big - 30.4MByte for Vol I and 28.2MByte for Vol II .
But, on the upside, they are in far higher resolution than the online versions. Indeed, they were of sufficiently high resolution to allow us to save them out as plain text using Adobe Acrobat Professional (V6.0.5). That was a surprise and a delight but, we suspect, not necessarily something that will be true of all PDFs downloaded from Live Search Books.

Foreword of Mark Twain's Letters in downloaded Acrobat version
(click for larger image - to see 100% view on 1280x1024 screen)

Foreword of Mark Twain's Letters in downloaded Acrobat version
(click for larger image - to see 125% view on 1280x1024 screen)
However, anyone who'd wanted simply to read the text or copy sections of it - rather than look at the original printed page and photos - would probably opt to download the plain-text-only version available from The Internet Archive. This contains both volumes and weighs in at a mere 1.59MB.
It's worth knowing, though, that the punctuation in the version we saved out looked to better represent that of the original - as did the line-breaks and paragraph-breaks, making the version output from Acrobat a lot easier to manipulate within a word-processing program such as MS Word.

Foreword of Mark Twain's Letters in plain text created by
Adobe Acrobat Pro 6 from the downloaded Acrobat version.
Note that there are paragraph breaks and that
the line breaks accurately conform to those of the original
(click for larger image - as seen on 1280x1024 screen)

Foreword of Mark Twain's Letters in plain
text - downloaded from the Internet Archive
(click for larger image - as seen on 1280x1024 screen)
But, whatever caveats we might have about Live Search Books in its beta form and so soon after launch don't change our original opinion that it's a massively useful and enjoyable tool and very warmly welcome.
That said, the Google Book Search find-libraries feature is kind of wonderful!
But, if you want access to a book now, then Live Search Books' ability to read or download gives it a big advantage. However, in terms of the number of available books, it can't yet compare with The Internet Archive and its plain-text offerings.
Thoughts on online access to books? Let us share them in this thread in the HEXUS.lifestyle.news forum.
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HEXUS.links
HEXUS.community :: discussion thread about this articleExternal.links
Microsoft - Live Search Books home pageGoogle UK - Google Book Search home page
The Internet Archive - home page