I've run into similar problems in a site where I'm using the editor as well.  However, I've got users with all kinds of browsers using the site.  They load a page with the editor and many times it is snappy.  Other times the same page will load, but they will wait for a while in order to be able to actually edit content in the site. 

 

I'm going to give the image editing a shot and see what happens.  I started to apply the same switch from .png to .gif across all of the various loaders and discovered that blank2020.png is only in the IE loader.  The other loaders all use the blank2020.gif file already.  So, that makes me think it may do something for IE, but I'm not sure what to do with the others.

 

Interestingly enough, I can manifest a problem in my development environment pretty quickly.  I load a page up a couple of times through Visual Studio.  By the 3rd or 4th trip I'll get my development environment to basically hang waiting on these files to download for the editor to activate.  I end up having to kill the debugger instance and relaunch the site, on which everything works ok for a bit, then will eventually come to a screeching halt in Visual Studio again.