Michael Gray explains why PageRank sculpting is important. He explains that Google has downplayed the use of PR sculpting but it seems that it's working pretty well for some people. Using an analogy with two very different cars (one, an old shoddy car; two, an expensive powerhorse) he says:
The links on your website are touch points between your website and Google’s crawling and indexing spiders. Much like cars not all websites are the same, not all websites have the “horsepower” to take advantage of tactics like nofollow and pagerank sculpting. The key is figuring out if you are closer to the Ford Gremlin or the Ferarri Enzo and adjusting your strategy accordingly.
Indeed, many forum members agree that PR sculpting is beneficial especially for small sites where you can drive the link juice to the proper pages.
In a second thread, PageRank is dissected by Ann Smarty at Search Engine Journal. Ann summarizes a WebmasterWorld discussion about the Graybar and how the PageRank toolbar, if gray, can mean two things: either the site is broken (not SEO'd) or the site is penalized. She also discusses some myths and truths regarding the gray bar. Some items of note include the fact that the gray bar is not equivalent to PR0, it actually doesn't mean the site is deindexed/penalized, it can indicate improper behavior, PR can change with no impact on performance, and more.