Like most things technology, such as Web services, getting the granularity correct is difficult and can make the difference between success and failure.
I am trying to balance what goes where, when I look at Twitter, facebook and Blogger (my tools of choice right now).
With Social Networking tools, I see a disconnect in how some people are using them. I use that phrase carefully as I don't think there are really any rules to follow (which makes this my point of view).
When you have a mismatch in granularity between readers and authors, people will dismiss micro-posts as not well thought out and a waste of space. At the other extreme if people are expecting nibbles and get a four course meal, they will generally skip it.
If you set expectations then people are more forgiving..
Twitter
I'm still trying to work out where Twitter fits.
First, I think of twitter as micro blogging, you are limited to 140 characters for each post, so you need to keep things short and sweet. The audience is somewhat different as well. While you can limit readers to only those you allow, most people appear to let anyone in. (you can flip this around and lock down Twitter and let anyone read facebook, but that is not typical).
If you are going to follow someones tweets, you need to have a good mental filter. Once in a while you will get a nugget of connectedness, but don't make it your job to carefully parse though looking for pearls of wisdom.
facebookGives you more room to post and is aimed more at social friends. I think this is more for the "think for a few minutes and post " granularity. You generally have a smaller circle of friends who are listening, so you hope that they actually are somewhat interested in what you are doing.
I do see a disconnect sometimes when folks use twitter and automatically post to facebook. I'm ok with using the tools to do different jobs, I just think sometimes that some tweets are not facebook worthy. Maybe I am not a worthy friend?
If you do have a facebook friend that tends to post their hourly status, you can ask facebook to show you less posts from them. This is less extreme than un-friending.
BloggingThis is for the longer discussion. This one took me about 30 minutes. I was going to say "well thought out" posts, but I'm not sure this is quite there.
The "well thought out" issue is an intresting one. If you over think it, you never post anything (see earlier posts). This is actually one of the things I like about facebook, it has given me an outlet for the less intellectual stuff.