I, too, have this problem with 2.8, when my site is viewed in either IE or Firefox:
* Can't drag Widgets around.
* Can't drop-down Widgets that are on my sidebars.
Funnily enough, the page scrolls down when I attempt to drop-down a Widget that has (IIRC) a long setting panel--apparently, the Widget IS trying to open, but on some invisible "rendering layer" in the browser.
I wouldn't even have noticed had the installation not deactivated my Collapsing Links widget--all others migrated fine (and I'd bet it would, too--it's pretty darned simple). So I consider this problem as having an installation bug as well: there's no reason to remove a Widget; just let it mis-render if it somehow is made obsolete by the update, and hopefully the widget author will update it (and I can then "fix" the problem with a mouse click).
For the record, I use a mix of hard-coded sidebar elements (in the sidebar.php file itself) and widgets managed through the WP Admin tools. It's the only way that I can control the Meta info (I'd prefer not to WP brand my whole site, thanks) and use two instances of WP-Cumulus (one for Categories, one for Tags).
I've otherwise been delighted with WP--after all, this is my first "bug report." Bravo!
...But, like, please fix this fast. I use my Links a LOT, and now I have to hand-code them into the sidebar.php file, which will be quite ugly (for one, it's LONG). Thanks!