I just started an account with Shelfari - I was looking for a way to show what I'm currently reading in an easy, but more aesthetically pleasing way. So far, the aesthetically pleasing bit seems to be working okay - the widget doesn't seem to be distorting my blog, the book covers are nice, and the title and author text fits well enough. As for the easy part, I had some problems figuring out how to get Shelfari to display what I want it to display, and it froze when I was editing the books in my list. However, it might still turn out to be better than my old method, adding and subtracting books in a blogger text list. I briefly put the Shelfari widget in my other blog and discovered that just by editing my book list in the Shelfari website I edit what's displayed in both blogs. That's great and removes the need to do the same edits two times, once for each blog.
I'll try out Shelfari for a while on this blog (a while might be as long as a month or as short as a day), and, if I like it, I'll keep it and add the widget to my other blog.