"Blogs will save democracy." - random blogger
While there are many blogs about blogging, and in general the concept is overhyped, blogs do present a solid marketing opportunity.
Gaining unrequested links usually takes a good bit of effort. You have to be one of the leading resources in your field, you have to provide something that others do not, you have to give others a reason to want to link to you. Some people try to buy their way in, but of course that eventually backfires.
With blogs you can just whinge on about whatever, and so long as it is usually on topic some people will read it. Sometimes the smallest things, like mentioning a 20 pound AdWords coupon can get you multiple free links from other regularly updated channels, and the attention of people who read those channels.
If you are looking for resources to cite you can use a tool to look at topical trackbacks (which also point links your way) and help get you noticed by some of the leaders of your community. Of course you can go too far and be labeled a spammer so you want to use some caution / restraint.
Some systems, like PubSub, also show you how citation data / linkage profiles change over time. If someone is linking at a competing channel then you can ask them to link to yours, or reference them, or make a useful comment on their site which is likely to get them to click through to your site.
Some bloggers also tag their content. Some have suggested using tagging systems for keyword research, but tagging is sloppy, narrow, and somewhat self reinforcing IMHO.
To me the real value of tagging is in linking opportunities and attention markets.
You can tag your content to work yourself into the tagged channels. Some people track certain terms, so you can almost guarantee they will read what you write if you tag it with the terms they track.
Of course, if tagging systems get too popular they will get heavily spammed. Technorati tags: blog, blogs, marketing, link-building, blog-spam, scoble, msn etc etc etc
For link building you can find people who are tagging things that interest you, make a good personalized proposal, offering something they are interested in, and get the link :)
Stuntdubl has a list of social bookmarking tools here.
