While I have only had WordPress 2.8 for a few days I have a brief review that I can give you.
I have all of my sites self-hosted on my own servers. I have WordPress 2.8 installed on each. The initial upgrade was not hard at all. I simply clicked the upgrade notice, and it started. The upgrade was done in minutes. I would guess that it has to do with database sizes, and such things that you have installed. I had no Plugin issues, so I lost none of the Plugins that I was using.
The update seemed to make everything in the Dashboard run a bit faster. One of the biggest improvements that I find is the NEW drag and drop interface for widgets. Now I can move widgets from sidebar to sidebar without having to retype the data that goes into them. There were other improvements made to WordPress. You can now search, download, and install Themes, and Plugins from your control panel. Another improvement is the screen options tab. Based on what part of the Dashboard you are in there are many options that you can control.
You can read more at WordPress.Org.
I am very impressed with this release. I am very happy that I did the upgrade.