cool, done it a hell of a lot in the last years. I have covered all of France, most of Spain, all of Germany... Im currently on the French German border after hitching up from southern Spain last week. its really easy, everywhere except southern Spain (we had mixed luck in portugal). there are certain areas to avoid, for example, Northern France can be a pain in the ass. On the west side, all roads lead to Paris, and it WILL drag you in. The center of France (Alsace/Lorraine) , can as well be really difficult, I guess with all the toll roads in France, a lot of people go through Germany instead. However, look at a map, consider junctions in highways if you have somewhere to be, and avoid/try to pass cities that are highway clusterfucks (Lyon or Mannheim are easy examples if you want to look at google maps for an idea...)
Also, take care of sparsely populated areas, for example, hitching in Sweden can be a pain in the ass if you get a short ride. Malmö-Stockholm is an easy ride to find, but if you accept a short ride and end up in Odensjö, you might be stuck for days.
Dont forget Hitchwiki.org, and be active with it to keep it useful and updated for the rest of us. If you have specific route questions, hit me up, or if you want to meet sometime, Im usually game.