Simple question as in title. What is the maximum number of posts that can be written in a blog?
There is no theoretical limit on the amount of posts that can be stored and served. However, there will be a limit on what your server can achieve, in terms of database size, hard disk space and processor capacity. On an ordinary dedicated server you should be fine as long a you stick with a couple of 100.000s of posts (I run an installation with 100.000 posts and 1.000.000 comments which is doing just fine).