So here’s a quick test to see how easy it is to blog using the iPad.
As an example, this blog post was written using the iPad and the WordPress app for the iPad.
The WordPress app allows for basic text entry, the addition of images, templates for posts and pages, and previews. One thing I am noticing is that, since my site theme is custom, the preview only displays the basic post text and not how it will look on my site.
Probably the typical use will be to sketch out a post idea, save it as a draft, then edit it further when you get to your main computer (or at least until you have access to a real keyboard) since typing HTML or doing anything fancy is not trivial using the virtual keyboard. Also, the WordPress app crashed in the middle of typing this entry, so you might want to save your longer posts for your main computer, or at least until a later version of the WordPress app.
Also in the course of entering this post and publishing with my iPad, it failed due to a collision with at least one of my plugins. So to fix this error, I saved the post as a draft using my ipad, then published it using my main computer. So, evidently, the WordPress plugin also has compatibility bugs with plugins used on your site.
So, using your ipad to draft posts for later publishing using your main computer seems the best way to go for now, and the best way to use the iPad to blog while mobile.