Just a week and a half ago WordPress for the iPhone was announced with a pretty killer screencast detailing what you could do with it. Tuesday morning it finally showed up on the app store (download it here), and I've had ample time to play with it. The good news is that it's very enjoyable to use and quite capable for creating posts on the go. The bad news? You've got to have an iPhone or iPod Touch to take advantage of it.
The key benefit to using this app is writing and publishing quick posts on the go. What I found after using it, though, is that it offers up far more to the discerning user who wants to use it as a very powerful publishing tool. You can upload photos either from your existing library or snap a quick shot with your phone's camera. I can see this leading to many food-related photo blogs. Also nice is that whatever you write can be saved on your phone, so you can work on dozens of posts at once and only publish when you want. There's also a great preview function that will show you what your post will look like without kicking you off to Safari.
I successfully connected two Wordpress.com hosted blogs to the app in just a minute or two, although I ran into problems connecting my personal hosted blog that uses the software install from WordPress.org. It's worth noting you'll need version 2.5.1 or higher to hook it up to a hosted blog, although updating to the recently released 2.6 is definitely worth it for all those extra publishing goodies.
Unfortunately there are some serious shortcomings to the iPhone that bring the app down a notch. If you're used to adding links to your posts there's not a lot you can do without copy and paste. HTML code is fully supported, so as long as you're good with your href tagging (which is brutal on the iPhone's built-in keyboard) you'll be able to add links from memory just fine.
Another quibble of mine is that drafts created on your computer won't show up in your post queue on the iPhone app, meaning you won't be able to start a post on your computer and finish it on the road. Ideally, future revisions will include better shortcuts for adding links and some support for fetching drafts from the cloud.
Hardcore users with a lot of readers will also be pining for some sort of comment management feature in future revisions. As it stands, you'll have to log in to your WordPress dashboard from Safari and administrate them from there, which isn't terrible, but it would be far more enjoyable to write and manage in one place.
All in all, it's off to a great start, and compared to competitor TypePad, which had its app available at the launch of the app store, WordPress is just as full featured and opens up mobile blogging to the millions of WordPress.com and WordPress.org users.
I've embedded screenshots and the screencast below.