I've been installing Dynamat (and Scoche's products) with excellent results 
for years.  I've found on the newer cars, the doors and rear wheel well areas 
are ideal candidates.  It's added weight, but does make a difference in sound 
level and quality. 

On Mk1 and Mk2, I recommend just about everywhere, 2 layers on the floor. 
On Mk3 and Mk4, generally doors and rear fender wells are all you need.   
Hatch area helps, but on newer Golfs/GTis, spray only... no other room to 
work. 

Some tips: 
1. Heat gun is a must.  Cheap is OK. 
2. Small wooden roller saves fingers. 
3. 2 layers are often better than one! (except for weight) 
4. On doors, do inside panels and outer door skin. 
5. Glue (hot glue) edges, and use duct tape. 
6. Take your time and do it right.  On average, when I sell these products, 
it's almost always over $300. worth (sometimes way more!), so it's an 
investment you want to do correctly to maximize results and investment. 

Hope I've helped, 
Mark Rosenkrantz 
Marker510aol