If it's something long like a full feature or book review I'll usually do it through Google Docs as I can edit it from just about anywhere then and send & share it to anyone else who might be collaborating or proof reading it. So in those cases it's really easy for me to keep track of any changes and revisions though when I copy it back in the WPUI, somethings the format goes a bit skew-wiff.
Anything short and punchy though, I use ecto, a mac based blogging app that makes spell checking, uploading images and bringing in flickr and Amazon associates content in, super easy though sometime's it does seem to have a mind of it's own—once or twice not saving a post which is very annoying.]]>
When I only want to concentrate on writing, I disconnect from the internet or close my browser.]]>