So, basically, if you're printing a book forget about softproofing?
On the Blurb site it says:
"Color Management: Controlling variables between screen and print
We’ve created this resource center because we understand how important your images are to you. Print on demand (POD) technology has come a long way, but still has a way go to match true offset quality. Results can be amazing, but getting an image you like – from your back-lit RGB monitor to a book printed on a CMYK printer – can sometimes be a challenge. Several variables come into play between your monitor and our global print network. In POD, books – covers and pages – are printed on different print devices, which means that even though everything is calibrated to the Blurb ICC Profile, variables are a given. Controlling as many variables as possible is what color management is all about.
With a properly calibrated monitor to accurately soft proof your images, using the Blurb ICC Profile helps you manage color more closely. Before embarking on setting up a color-managed workflow, please set your expectations appropriately. It is simply not possible for POD printers to duplicate the finely controlled color management that is possible with offset printing, so some slight hue differences may appear from book to book."
and
"The Blurb ICC Profile is based on the GRACoL2009 reference used in high-end commercial printing. Using this profile allows you to soft proof your images while in RGB or to convert your images to the CMYK color space of the print device."
Mike.
P.S. Sent an e-mail to the folks at Blurb Support to ask their opinion.