Using several browsers is what I do. It also helps to keep the changes looking right when you can view your site in multiple browser types.

On multi-user systems you can spawn a new browser as any user you have access to. I have several low priv user accounts set-up just for that purpose. The new browser window can then login as you wish and not clash with the others, even with the same browser type.

I would think even *cough* Windows 2K/XP *cough* *cough* could do that.(?) Can you make a shortcut or something that runs IE as a specific user? I know you do that for running MS Update (you folks don't really run your machine as a Superuser/Admin do you???). You should be able to spawn as many fresh browsers as accounts and memory allow.

For kicks I can pull up a remote session of a Win2K Terminal Server or a remote X session on *nix just to be sure my site looks right from another machine and IP. Pull up a few of those windows and you cover just about everything. Now if I can get my fingers on a Mac too.....