Phase 1, the original sites: Static content only.
Phase 5, about one year ago: Finally bit the bullet and adopted the Prototype framework. Life got a lot easier, but Prototype itself doesn't do all of the Ajaxy things that I like to do (like auto-complete-as-you-type, light boxes, fade effects, and so on). So I started layering different libraries, including Scriptaculous and MooTools.
Phase 6, about two months ago: I've found religion, and its name is JQuery. JQuery's elegance is so beautiful that it almost makes me want to cry. The documentation is outstanding. And it encourages community support through plugins, which quickly become indispensable -- stuff like auto completion, rounded corners, table sorters, tooltips, calendars, etc. And because the plugins are all based on the common JQuery foundation, they usually play nicely with each other. I'll be posting soon about how JQuery has made life much easier for me. In the meantime, I'm busily migrating all of my sites to it.