By default, WordPress gives you the following format: “http://www.yourblog.com/?p=123”, for example.
If you want to be more visible to search engines, change immediately this option! In this format, there is nothing except the name of your blog, which can be used.
If you chose the option “based on the time and date” the following format: “http://www.yourblog.com/2007/02/12/title-of-your-post/”, the engines will have important information to crawl and resgister in their databases.
It is always important to write “intelligent” article titles/Slogan with important keywords, which take information on the content of the post.