I am new to the forums, but I see a lot of post, people talking about Japanese knives, I by no means am the all mighty expert, but I exclusively work in Japanese Restaurants and only with Japanese Knives, so I had to abandon the western knives and techniques I had come to learn for a lot of them.
I mention the Gyuto first because most of the post are about this knife, I see a lot of threads say I need Japanese knives and they all fall short of mentioning anything but a Gyuto.
The Gyuto is modeled after western style knives, better known as the French Chef knife, if you have a French chef knife, you probably don't need a Japanese Gyuto. You will use them for the same task a person with a French knife does and I doubt vary much you will notice the difference performance wise. The only thing I will say about the Gyuto is that generally it is lighter, this can be a good thing or bad thing depending on your preference.
That being said a lot of the knives are different, Here are the essential three: the Deba, for example is used to break down whole fish, the yanagiba is for cutting thin slices of fish, the usuba, is used primarily for hard root vegetables. There are many other knives some for garnish, fileting eel, filleting octopus, fileting blowfish, variations on the deba for smaller fish, different types of usuba, the list goes on and on.
The cutting techniques for Japanese Knives are also very different, most are used with the index finger running parallel a top the spine of the knife, this is something they frown upon in culinary school as it can lead to arthritis and joint problems.
Then there is Carbon Steel, Carbon steel knives rust! You have to have extreme attention to detail with these knives to keep them in proper condition, knife oil and a rust eraser are essential.
Knife sharpening, sure the honing rod worked for your german steel knives, but they don't work for single bevel knives, at all. You have to learn how to use sharpening stones, and not the way I did, which is to say the wrong way from other chefs who claimed they know how to sharpen a knife using a stone.
If you want to learn how to use stones I recommend you go here to learn from an expert. He also goes over the different types of knives and what they are used for.
I don't know one person in all the Japanese Kitchens I've worked that actually likes the santoku. I don't know any professional chef in any cuisine that likes the santoku come to think of it.
I hope this helps.