Much of Dreamweaver's appeal centers around the Design View interface, which does a pretty good to very good job of rendering a page's CSS and HTML into a fair approximation of what the browser will display via the WebKit framework. Unlike a typical preview, web page authors can continue to edit the page content in this mode and, depending on settings, see placeholder icons for line breaks, positioned elements, code snippets, and much more.
Some users complain that Design View reacts so slowly as to become almost unusable and report having keystrokes take between two and three seconds to reflect on the screen. This can be due to one of several factors:
1) Due to the load of having to draw and redraw the layout and CSS styles as the author types content into Design View, Dreamweaver may become a little laggy. This information comes from David Powers (author of several books on Dreamweaver and one of Adobe's Community Professionals) in a slightly acrimonious Adobe forum thread. According to Mr. Powers:
Rules that apply to the <html> or <body> tags or that affect more than 10 elements force Dreamweaver to repaint the page completely.His solution is to make sure your CSS declarations are as tightly targeted as possible and use descendent selectors to tie elements into their parent containers. This is certainly good practice but may come as a rude shock to users who upgrade to CS5 from CS4 and discover their pages are not as editable as they used to be.
2) Although the listed specs are fairly modest, in my experience Dreamweaver CS5 requires a fairly fast machine and graphics card as well as a decently fast hard drive and RAM. If you are running on a slightly older machine any or all of the preceding could slow the program down.