As I see it, blogging isn't always about correspondence; sometimes it is just like keeping a diary, or a notebook for ideas that you want to remember. For an example of a rough and ready notebook-type blog, used for various purposes, see pab's potpourri.
Some personal blogs get shared with only a small group of friends. In fact, some blogging tools let you decide about each and every post whether to keep it private or make it public. For example, pab’s vox blog is currently private.
As far as personal vocabularies go, I'm convinced that reading lots of easy books (remember your book review assignments?) and writing lots of blog posts will:
- Refresh vocabulary knowledge that you have already,
- Increase the size of your vocabularies, and
- Eventually make it easier and easier to produce written ideas with the words you know and are still learning.