Facebook, Twitter and blogs are great platforms to share your life experience, make friends and market yourself or your company. But beware. Just because we now have additional outlets to share various parts of our lives, doesn't mean its appropriate to share everything.
Now a lot of this advice comes down to why you are utilizing these various mediums. If you are looking to log the daily goings-on of your life and are a stay at home mom or a working person who avoids talking about their job, then feel free to share. But if you're a recent graduate looking for a job, you need to be discrete about the photos you put on Facebook. Likewise, you ditch work one day for something fun--if your boss or co-workers read your blog, don't post your beach pictures.
You always want to be genuine and authentic, but when you don't know exactly who may be looking or reading, its best not to over-share. You've all seen the Facebook status or tweet that was too graphic or too personal. Don't be that girl (or guy).
The best rule of thumb is "Would I want my grandma (or grandpa) to read/see/hear this?" If not, it might not be appropriate. (There are always exceptions to the rule, the above advice is of course erring on the side of caution.)