The most recent release includes page-caching capabilities that are built in, which greatly increases scalability and reduces load time and server usage.
As far as user-friendly, WordPress always impresses clients - feels a lot like editing with MS Word, which most of them are familiar with.
Updating is simple - takes about 3 steps whether you use cPanel or not. Just backup the db, upload your update and click a few buttons.
I've also found WP to be excellent for SEO purposes - you can install the All In One SEO plugin and the Google Sitemap generator so that you control which pages are indexed, how they are titled, etc.
I would say, however, that WP may not be the best for ecommerce and if you want to use it as a full-blown CMS, you'll need to a little extra work in your theme development, but the online docs are excellent. You'll also find a ton of help just be searching Google.
I know Joomla is popular as a CMS, partly because it's crisp-looking - nothing negative to say about it, I've just come to love WP and use it for about 90% of my site developments now.
Well, it wouldn’t be entirely true if you say that Wordpress is a just a blogging tool. True! it is primarily a blogging software, but you can still use it as a (stripped-down) CMS . Moreover, there are a host of plugins that allow you to use Wordpress in a couple other ways than just CMS/blogging. At the end of the day, however, Wordpress is primarily meant to be a blogging system and that is exactly where it shines.
Joomla, on the other hand, is a full blown CMS. In fact, with the advent of Joomla 1.5 Joomla is an application framework. What that means for an average Joe is you can build any kind of web application on the top of Joomla. The CMS that comes with Joomla is just an application that executes on the top of underlying Joomla framework. You can easily strip this CMS layer away and build something different.
So everything boils down to:
If you need a blogging system: use Wordpress.
If you need a simple CMS: you can still use Wordpress.
If you need a full-blown CMS: go for Joomla.
If you want to build a custom application while still leveraging the functionalities offered by core Joomla framework: build you application on the top of Joomla.