I used to run a myspace layout website and couldn't quite figure out how I got a PR of 3 or 4. Thinking back I realized I had exchanged links with every MySpace Top Site website. If your website is in a popular category you might just be able to get a high PR by finding all the topsites in your category and trading links. Here is an example of one of the websites I traded with: http://www.myspacetopsites.com/
Plus submit to directories, bookmark, comment and you will get even better PR, I got pr 3 just for link signature, but SEO is not all about whats your pr.
i dont believe in your statement that you can get high Pr from social book markings for mostly Social bookmarking site has a no follow attribute..
I have many sites for which google shows lots of backlinks from social bookmarking sites when we check at webmaster account.
Directories only seem to work if they are "niche" directories. Sometimes it is hard to find a free directory that is specifically for your niche.
I would only trade up for link exchanges. If you have a PR3, then trade with a PR4+. Social bookmarking sites are good if you have an interesting, valuable website. Then others in the networks might link to your website. Most are nofollow and won't pass page rank directly. Make sure your internal link structure is set up properly to get the most bang for you buck from each website that links to you.
but remember now a days PR is not so important U should try to get better results in the SERP so that you can get the benefits
There are two types of PR, and theoretical PR is still very important. The toolbar PR doesn't matter much, but it does relate to the theoretical PR that Google actually uses to determine the value of a given link and it's anchor text. The Google Directory actually ranks websites on toolbar PR, and lately I've seen some of the Google Directory listings showing up in the regular Google SERPs.