Some of the my considerations before choosing to switch from :mt: to a different blogging engine.
Currently, :mt: generates a static file for each post I publish (strictly speaking, actually this is a number > 1 since I use all of :mt:’s archiving features and each archiving method generates one file). On PHP-based systems, each post that is stored in the database is pulled out and reformatted on-the-fly appropriately depending on user requests. As a result, there is no delay in publishing. Furthermore, there is the option of publishing at a specific time.