I have made a few blurb books, and I am currently heading a teamm making a new toycamera book using Blurb (toycamerabook.com).
The premium paper is the way to go. It is thicker and significantly nicer. If you are planing on having photos both on the front and back of each page you pretty much have to use the premium paper. The normal paper is basically see through. Images on the back side are visible from the front. This is still true with the premium paper but it is not nearly as noticeable.
As stated earlier, Blurb is not a tool to make a very high quality book. And to make a pretty decent book it ends up being very expensive, but it's a pretty nice tool for what it is.