My wife and I just returned from a 3-month self supported tour through seven European countries. We pretty much rolled our own as far as route planning goes for the first half of the trip. My GPS, a Garmin 60 CSX, was invaluable throughout the trip. I had Garmin Europe Maps loaded on it as well as in our netbook. It saved countless hours navigating through the larger cities, finding alternate routes, finding campgrounds, and finding hotels. It has a very comprehensive listing of campgrounds and hotels in the program. Even when we hit countries with established bike routes, it was still a great tool. A lot of the bike trails are not on the Michelin Maps (which is another great tool), and it helped when alternate routes were needed because of muddy roads or finding an alternate route to a town. The bike routes were designed for touring, and were not necessarily the shortest way to get from point A to B.

It was also fun to see our track through cities, and know what the elevation profile looked like for the day. It helped to explain why it took us 2 hours to get through some relatively small cities. It also confirmed our perception that there is really no such thing as flat. We had several days in Holland where we climbed over 2000'. It is also great for finding your way back to a bus stop or hotel when playing tourist in the larger cities.

If you are an ACA route, there is probably no need for one. But if you want to explore, and make your own routes it is a very useful tool.

P.S I also use it ( in conjunction with maps) as a backcountry ski patroller, and while ski mountaineering and backpacking. Before I retired, I also used it for work.