To see how important PageRank is, offer a link from a PR 8 site to a group of seos and see how many turn it down.
LOL. "How important is PR" could also be answered a number of different ways. "How important is PR do search X". "How important is PageRank as a marketing tool for Google". "How important is PR to me if I sell links...err sponsorship... on my site".
Each has a different answer, each has a different perspective.
For an individual page, the answer is that PageRank is important, but no more important than many other issues (like using teh right words).
As a quick lisyt, PageRank helps:
1) Rankings on all SERPs, but on competitive SERPs the most (e.g. news, car, mortgage etc).
2) Frequency and depth of Google indexing
3) Google market their site better
4) Site owners sell links for more
5) Others profit, by charging higher prices for a service of dubious value (link purchases, exchanges etc)
6) Getting people all worked up. "My PR went from 6 to 5, why does Google hate me"? Ignore this.
PageRank is great, the more the better. Some people are of the "it is not right to chase PageRank" school, but there is nothiung inherent wrong with doing so. That said, what emphasis you
personally place on chasing PageRank, and what methods you subsequently use, is dependant upon what you feel is more rewarding, and indeed your own personal strategy mix. For small sites, it may be vital to get a few extra links, butfor big sites (e.g. CNN) it is totally irrelevant. Some sites will simply need more PageRank to do better, others need better content. On-page optimisation is always the easiest form (you have direct control), but that doesn't mean it is the best or only form.
So, don't discount PageRank. IMHO it is more than just a tie-breaker, but it will never replace entirely on-page SEO. Just don't obsess about it, there are far more important issues (like whether Australia get a bonus point in teh One Day international against Zimbabwe, what I have for dinner tonight etc etc).