Why is scrolling in design mode with Dreamweaver in CS4 on my Mac so slow?
You should first check if you have enough ram to run all the applications. It does sound like a refresh issue. Do you experience that problem with other memory intensive software? does it only happen on design mode? Is it running from an external drive or retrieving pages and images from an external drive?
Dreamweaver is a pretty large and bulky application, so periods of slowness can be expected from time to time. This will especially be true if you have a lot of other applications running at the same time. It could also be some kind of bug in the software, which could possibly be fixed through an update/patch.