Is there a way to add shortcuts to open a particular folder in Save Dialogs and Finder Windows? I know that when you're saving or opening a file ⌘ shift D shoots you to the Desktop folder, and pressing ⌘ shift D whilst using finder shoots you to the desktop folder as well. 

Is there a way to create a custom shortcut to jump to your own choice of folder? (e.g. ⌘ shift W for your 'Work' folder).
By default, no.  What I've done is drag folders I access frequently to the Places section in the left side bar.  There is software to accomplish this though.  Default Folder X does this, and more.

If you're in a save dialogue you can press / to get a file path dialogue, or press ⌘+Shift+G to get a "Go to folder" dialogue.