I haven't experienced any slow downs, either, on my mac. (Mac Pro 15 with 2.53 Ghz Intel Core 2 Duo and 4 GB of memory).
I have had less powerful macs before and didn't have any problems either. Do you have at least 2 GB of memory... if you had say only 1 GB, there probably is a threshold for speed somewhere between 1 and 2 GB on Dreamweaver because Dave said, they are memory hogs.
If you do have at least 2 GB of memory, there may be something else going on with your machine. Are you running any programs that start up automatically and run in the background? To give you an example of what can happen, one time I found out when running Pro Tools (another memory hog) that you had to shut down Blue Tooth as it interfered with Pro Tools. While I know Blue Tooth doesn't cause a problem with DW, maybe you have installed something else that does.