To the OP,
You made some good suggestions, but there is a lot more to it than just 'link building'.
First of all, your links must be relevant. If a site about dog food with a pr5 is linking to your site which is about business, then Google would see this link a non relevant, giving you basically no value at all.
Then there is the issue with the rel="nofollow' tag. Most directories will link to your site, no problems, but they will use this 'rel="nofollow' tag which prevents the
pr from passing on, making this link useless. This applies to all links.
If you can find a linking source which is relevant and has good
pr, you need to make sure you use the appropriate anchor text. Usually a keyword term you are targeting. Once again, this link must be followed or it will be deemed useless!
As Vidiky pointed out there is 'on page' and 'off page' optimisation. You need to make sure your 'on page' is spot on otherwise all of the work you put into link development (off page) will be a waste of time as your website will leak all of the
pr you are trying to build.
Think of your site as a bucket, with hundreds of holes in it. No matter how much water you pour in, the water will just keep running out!
I hope this helps.
Business Trader