For a long time the grey hat and black hat communities used sledgehammers to crack peanuts, spamming out thousands of blog comments and forum profile links using software made specificially for that purpose.
However, the times are a changing and with those changes the good 'old fashioned' white hat techniques are coming back into fashion.
Yes, I'm an advocate of writing remarkable content, publishing it on high page rank authority websites with an author link or contextual link. This is often referred to as Guest Posting. A solid technique that is virtually unbeatable.
Some people had tried to take this technique and make it a mass-blast approach by forming blog networks which take one good article and spin them, using synonyms, into dozens or hundreds of unique versions. The output is 99.5% garbage, barely readable, and far from remarkable. So, it makes perfect sense that Google would devalue these, as witnessed by the 700,000 site owners getting notices via WebMasterTools!
There are other ways of building authority links to your website on high page rank, dofollow sites. The finding, and selling of these, has been the mission of Angela Edwards for several years. For a small monthly fee, she sells a list of 30 such sites to her subscriber base, which some say numbers in the thousands.
How is this different from just blasting blog comments or xrumer forum profiles?
Quite simply, these forums and community sites will often require participation in order to get the most of it. Simply registering on them is not enough to get any real benefit. Instead, one must register, post, comment, view, contribute, add value, and help make it a community.
An example? The obvious one is this site: my.opera.com
Long time users who regularly participate and add value to the community will find that they have accumulated a number of links back to their blog, profile and photos on the site. These pages, in many cases, have great page rank authority, and will help the author make their mark on the interweb.
The moral of the story? Don't look to get something for nothing and be slapped by the karma police. Instead, engage, participate, give back, pay it forward and you'll be rewarded commensurately.