When you access the reporting services over SSL you can have the problem that the reporting services GUI under IE is very slow.
The solution is quite simple: Login with the servername or domain name. E.g: SERVERNAME\username
This problem exist under IE 8 and IE9 under Server 2008, 2008r2, Vista and Windows 7.
I had the same problem, your solution worked, I investigated further and found that removing from rsreportserver.config fixed it without the need for users to enter the server name or domain during log in.
Thanks for your post.
Tnx Steve for your feedback