Does this happen even on a local drive, when going between C:\ and C:\Users, for example?
Does it happen when in Details mode, or only Thumbnails or other modes?
If you open up Task Manager and look at the CPU usage, does it go up while Opus is changing folders?
Try turning off all file display columns except for Name, then turning on the Format Lock (click the lock icon on the status bar) and then change folders again. Is it still slow?
If it is still slow in all of those cases then the most likely causes I can think of are:
[ul][li]Something in your toolbars / menus which is triggering a lengthy action each time Opus refreshes whether each toolbar button should be enabled. (e.g. If something on the toolbars is pointing to an unavailable network drive, it might cause that.)
[/li]
[li]A shell extension installed by something else, which is hooking into Opus and causing a delay for some reason. (e.g. We've seen some shell extensions which hit the network when they shouldn't.)
ShellExView can be used to see which shell extensions are installed and disable them to see if they are connected. The guide to troubleshooting problems when changing folders has a bit more information on that, as well as some other ideas which might prove useful.[/li][/ul]
The general slowdown or instability investigation steps guide has more suggestions if neither of those seem to help. Each of the suggestions has helped someone in the past, but it's hard to know which might be relevant to your machine.