I have several PR5 sites after 2005, and I figure out that paid links are the most effective ways to get on-way inbound link.
My group has a site about futures trading, its PR now is 2. At first I found it not really hard to get PR. It got PR 3 in the three first month we work on. We care about it regularly but the PR cannot get better, even down to 2. I don't know what we did wrongly. To get PR5, it's our dream
I wish that I have started on early with this. The highest that I got till now is just pr 2 from 3 of my sites.
I very much agree since 2005/06 it has been that much harder to achieve a PR5. i used to have a 3 PR5's these then all dropped to PR4. I find getting a PR3 fairly simple its just that step up to Pr4 and then eventually 5 is proving difficult when attempting to achieve without high costs incurred e.g. not buying links or hiring others to post for you. PR5 can be done but with a lot of work.
I achieved a PR5 within the last few years, it went down but its up to a PR3 now and i believe i could nudge it to a 4.
I have several sites with PR5. It's not rocket science. You just need to spend more time or money to get high quality & strong backlinks.