Layers is a different design environment to the standard table structure of a web page.
They are very good from a designers point of view, but the browser relationship with them is definetly, a major consideration, you can see massive differences between IE, NN and the WebmasterWorld favorite Opera. That is definetly something to take into account.
If your looking to get into layers, then the tutorials on the DM software is basic, but a reasonable introduction, the manual is good as well. Its worth reading about layers themselves, in the various forums in WebmasterWorld that deal with them. Their are loads of tricks from an SEO stance that one can do with layers, but watch your back if you decide to do them - search engine wise.
From a DW point of view the visual environment is very good, but as with all other wysiwyg's DM will add unnecessary code (non-validating). I do have to say that doing quick sketch outs of sites, i like to use layers for speed, but when it comes down to publishing sites, by far i prefer tables, SE's still read pages around HTML3.2, though some are going beyond this now, until a universal standard of SE's at least parsing HTML4 structured pages, i will be staying away from layers from a published point of view.