Most blogs are NoFollow, by default. This is mostly to decrease the amount of SPAM interfering with all our lives. (I'll give you links to more information later, so chill and just read for now.) PageRank (PR) is important to bloggers and webmasters - it tells the universe how credible your blog is. PR0 is the lowest ranking, while PR10 is the highest. Most blogs/sites are PR3 or below - and you can count the number of PR10s on both hands. Adobe, Google, and similar sites are able to achieve a PR of 10...where most of us - even when a blog is as brilliant as The Queen Speaks - will be lucky to get a PR of 3. A PR3 means you are doing very well for yourself.
PR is also important in regards to where search engines "rate" you. Sure, backlinks are important in determining PR - especially backlinks from sites/blogs with a high PR. The same goes for DoFollow - it is much better to have a little love from a site with a high PR than it is to have quite a bit of lovin' from pages with a very low (or nonexistent) PR. (Funny thing is, I had a PR3 on The Queen Speaks for a long time - around 1.5 - 2 years...then I start posting more often, and doing things to actively promote my blog and make it better - and Google slams me with a PR0. What's up with that??)
Some of the PR game is left to the Internet Gods and whatever mood they are in when ranking your page...but there are some things that will definitely drag your PR down. On the plus side, there are other things you can do to make these same Internet Gods smile upon you, hopping up your PR.
In order not to confuse myself, I'm going to stick to what NoFollow/DoFollow means to you in the scope of comments and PR. So here goes:
Some bloggers choose to give readers who comment on their blog a bit of automatic lovin' - by making their blog a "DoFollow" blog. What is a "DoFollow" blog, exactly? A DoFollow blog gives you some bloggy love by providing a backlink to you when you comment. So basically, commenting on a DoFollow blog is better for you than commenting on a NoFollow blog...*IF* you are interested in increasing your PR and making it easier for others to find your blog in search engines (and therefore, increasing your traffic). If you are only interested in Grandma Phoebe and Aunt Sally reading your blog, then there is no reason to worry about whether your blog is DoFollow or NoFollow - or your PR.
If however, you want to increase your comments - which is a result of increased traffic - then changing your blog from NoFollow (which it probably is now), to DoFollow may be a good decision for you. As a side note, it is important to realize that DoFollow only works when the name and URL are placed in a comment. If you choose to comment under your Blogger account (or any other account), you will not reap the benefits of leaving a link on a DoFollow blog. It isn't necessarily a bad thing - your comment will still show up. The only difference is, without using a name (usually the site's name) and typing in an URL, there is no link love given back to you for commenting. In an effort to reward those who comment on my blog, I have changed The Queen Speaks from Blogger's default of NoFollow. This is now a DoFollow blog - which is why I have placed the pink badge in my side bar. So comment away - and enjoy the lovin'!
This is only a quick overview of NoFollow and DoFollow. There are staunch arguments for having your site/blog one way or another - and further research really should be done before making a final decision.
You can read more about NoFollow and DoFollow at these websites:
(See? I told you not to spaz out, that I would give you more information!)
Wait! Please remember...I am only supplying information. And this information is being dispersed out into the universe as I understand it - which does not mean I'm totally correct. (Remember, I'm way non-technical!) I do this to try to help fellow bloggers - and I seriously advise you to do further research at the links I've provided (or your own) before deciding what to do. YOU are responsible for your blog - and all decisions regarding it. Please don't write me and complain that because of my information, your life is screwed. I won't know how to fix it. Hell, I have a hard enough time keeping my own life straight! xx
EDIT: There is a great article on another blog I would like to point out to you. For more information, please check out the post written by Nicolas Prudhon, DoFollow and NoFollow Attributes. It's definitely worth the read!