Let's say I have a blogspot blog, and is about Cars.Do I have to submit my blog to Blogs Category, or for example to Life>Cars ? Do directorys accept blogspot blogs ?
In my directories, I tend to add all blogs to the most appropriate subcat under the blog category. But check the guidelines of the directories that you submit your blog. Some will mention how they treat blogs.
It depends on the directory category structure. On my blog directory(see my sig), your car blog would be put in "automotive"
With me it would depend on the nature of your blog. If you talk more personally about your experience with various cars, I would put it under blogs, but if you simply use blog software to essentially make a site that gives honest reviews of cars (more business related), then I would place it under autos. Of course with some directories (like mine), the point is moot since I allow multiple submissions. In my case you could be under both. As for blogspot blogs...I'll take them if they look like a real site. On the other hand, if they are simply thinly vieled doorway pages for your affiliate site, I reject them.
Blogspot blogs tend to be in a subdirectory of blogspot, rather than having their own domain names. A lot of directories do not allow free submissions of anything but the root domain, so check the guidelines first. Part of the reason for this is that people set up sites on free hosts at the drop of a hat, and forget them just as easily. Blogs would be a good example of where this was common. I once came across the statistic that most blogs get an average of one post before being abandoned. That was some time back, but I have a feeling things haven't changed all that much.