My opinion

I believe the official difference is that a blog can be about anything the owner likes, and he/she has the final say on what is acceptable in the resulting discussion.  "My blog, my rules," basically.  A thread, on the other hand, seems to be more democratic and should be more train-related.

For me (not being one to go on about non-model railroad stuff here or to lay down the editorial law too much) I find that a blog is a lot easier to find a few months down the road when I'm ready to update the status of a project.  Also, I use a blog as what the name suggests - a web log of some project or theme, whereas I see a thread as a topical discussion of some model or prototype related subject.

But that's just my two cents' worth.

Drupal Blog

The "blog" option in Drupal (the software MRH uses to manage the forums) is simply a way for an author to organize their posts in a chronological order.

A blog post is no different than starting a topic except that the collection of "topics" can be viewed by clicking the "view so & so's blog link."

So for example, if you are chronicling a layout construction, do it in the blog section and you can then see all your posts together and share that link with your fiends.

ie: my blog posts: http://model-railroad-hobbyist.com/blog/23320

or Ken's blog posts: http://model-railroad-hobbyist.com/blog/11972

Blogs are a diary

but, and I'm sure we all have run into this, you Search the internet and find what your looking for on a blog, only to see that it's from maybe 2008.  You follow along and see the progress, then you notice there is more and more time between postings, then the next thing you know it's 2011 and nothing new has been posted, and you're left hanging.  If you post a question on something you saw, chances are the owner of the blog isn't even checking things anymore.