PageRank is not the be all and end all of Search Engine Optimisation, but it is certainly something that can be utilised by any site owner to drive the importance of certain pages.
PageRank demonstrates the value of inbound links to a site, illustrating a rating out of 10 for every site on the web. The highest ranking being 10 reserved for high authority sites such as www.google.com, www.w3.org and www.cnn.com, these sites have worldwide interest and this is reflected by the willingness of web users to link to them generating massive amounts of trust.
For an SME to have anywhere near this amount of PageRank is unrealistic, but even with a PageRank of 2 or 3 you certainly have the potential to exploit that small amount of authority.
Your website will have a natural architecture that will be viewed by the search engine robots when they crawl the site. From this an amount of PageRank will be determined from quality and quantity of other pages both internal and external that link to your site, this is where you can take advantage of PageRank to ensure each page is acquiring the ideal amount of authority.
By identifying the pages within your site that hold the most PageRank, you can start to build a hierarchy of pages, with the homepage normally at the top. From this you need to make sure that at each level you have some relevant keywords being targeted on each page, and more importantly that internal linking is promoted from these pages to other key pages (using relevant anchor text).
By ensuring that all pages of value are benefiting from worthwhile content, whilst linking to other core areas of the site you will be creating a web of high quality linking, and at the same time improving the user experience.
