Just a quick reminder to anyone out there that may not know.. Enabling the Visual Editor in your User Profile settings gets you access to both Visual and HTML editors in the Write/Edit Post screen. Just click on either tab above the toolbar to toggle between modes. So you can write your posts in HTML and then jump into the Visual Editor to take advantage of the new Linking tool, which makes adding links incredibly easy.
In previous versions of WordPress, if you enabled the Visual Editor via your User Profile page, that's pretty much what you were forced to use. There was no way to leave it enabled and then just choose your preference locally from the Write/Edit post screen, so every time you updated your post, the editor would switch back to visual mode – even if you repeatedly click the HTML editing-mode button. Older versions of WordPress were like this for quite awhile, and during that time many WP peeps just decided to disable the Visual Editor to avoid the headache and constant switching.
Above is a screenshot of the User Profile page of version 2.3.3. At some point, it switched from "disabled" to "enabled", as shown below for WordPress version 3.1.2:
Fast-forward to WordPress 3, and welcome the new streamlined Linking Tool that only works in visual-editing mode. It's an awesome tool that makes internal linking almost fun, but unfortunately it is not available with the HTML editor. So all of those seasoned WP users who've been conditioned to disable the Visual Editor during setup are now completely missing out on the awesomeness of the new Link Tool.
I don't know when it happened (which version), but somewhere along the way, WordPress started remembering your editing preferences right there in the Write/Edit post screen, so it's no longer necessary to "Disable the Visual Editor" next time you're setting up a site. Sure you can still disable it if you want to, but why? Leaving it enabled gives you the option to choose which editor to use while actually writing your post. This gives you access to WordPress' new Link Tool without sacrificing your ability to compose in HTML mode.
Then again, I may be totally wrong and everyone already knows about this. I hope that's the case, because the new Link tool is super useful and worth a quick jump into the Visual Editor.