I had forgotten all about this issue, but was reintroduced to the Dreamweaver Slowdown after installing it on a new system drive. On opening an old document, typing slows to a crawl, even when there isn't much on the page.

The answer is to install the updater, located here. This updates Dreamweaver 7.0 to 7.1 (on a mac at least) and apparently fixes the slowdown. What it does NOT fix is some funky aliasing around letters upon selecting text.