The only modules I have installed are: DOM, UserDefinedForms, Uploadify plus the standard SS installation.
I don't have any custom JS in the CMS. Just using some DOM and HasManyComplexTableField instances here and there.
Some more insight... I removed the line like you suggested and reloaded the CMS. Surprise, no problem this time. However I was logged in already.. maybe this issue only surfaces when you're logging in. Also, I didn't see an assets/_combined_files/ folder... this tells me it's probably not being generated.
You won't see the folder via the cms, but you should see it in the file system. If it's not on the filesystem check your admin permissions - make sure your web user can write to the folder. i.e http://www.silverstripe.org/assets/_combinedfiles/leftandmain.js
Yeah I was looking in the file system to begin with.
I set the assets folder perms to 777 and still don't see the _combinedfiles folder. Perhaps I need to create it and set perms on it first?
Another insight... I don't get hit with the loading hang anymore, even when I log out and then back into the admin.