As a wordpress site grows, database performance decreases significantly.
A wordpress site that has hundreds of posts will experience high server loads caused by poor database coding. However, forum software that uses mySQL can have hundreds and even thousands of posts without such noticeable defects in database speed.
I wish that WordPress could take some database structure cues from popular forum software manufacturers such as vBulletin, Simple Machines, myBB, and phpBB.
In order to duplicate poor performance associated with poor WordPress database coding (even on a dedicated server), it is recommended to make use of plugins that translate RSS feeds into WordPress Blog entries. This will allow the creation of a lot of blog posts within a short period of time. As the database grows, attempt to create a hand-written blog entry. You'll notice that it takes WordPress several minutes of processing time (accompanied with high server load) before you can begin writing your post.
Of course, if you have a blog that has several dozens of authors generating pages upon pages of fresh content, you'll also notice that it takes longer and longer to publish an individual post.