Wordpress limits - system design consideration

I have had some pretty good success using Drupal. If you aren't trying to build a blog there are much better things out there for dynamic CMS. Wordpress is a great piece of blogging software. Try to make it do something else? It becomes a big pain to do. Having developed "applications" in both. If a blog is not the primary component (which a news site would also follow suit) then use a true CMS and not a blogging platform.

WordPress places no maximum on users, posts, etc. beyond that of the underlying technologies (your database, mainly). WordPress.com runs on the WordPress MultiUser platform and it has six million blogs, a billion monthly pageviews, and 200k new posts a day.

Your limitations will be more structural - WordPress is designed first and foremost as a blogging platform. If its interface and methodology fit your project well, go for it, but if you're going to be hacking the shit out of it, a more generalist system like Drupal may suit you better.

If it's a blogging platform you are designing, then WordPress should fit you needs. You can also look into Movable Type (Perl).If you are looking for a Content Management System (CMS), then you should look at Drupal and/or Joomla. Movable Type is actually starting to integrate with Drupal.

Wordpress has some performance issue, about a dozen pages/sec in default setup. But using plug-ins like SuperCache, it can get it to scale pretty well fairly easily. You can do anything you want with a custom "theme". But WordPress isn't going to manage the content in the "theme" for you, just display it.