Major issues over here, wet roads with lots of salt during the winter...:
1. The aluminum bearing blocks inside the rear axle corrode due to galvanic corrosion. Corrosion stops if the blocks are soaked with engine oil but it lasts only about a year. Covered by the corrosion warranty but not very likely to fail before the warranty has expired.
2. The hooks carrying the exhaust system rust away long before the tubing is gone. 3:rd part clamp-on spare parts are available at least over here.. Some grease on the hooks solves the problem for a while.
3. Lower front spring seats rust. Dig out the dirt and pour some engine oil in them and they are fine for at least a year
4. Rear brakes.. if you drive in an energy-saving way (as I do), discs and calipers suffer badly from rust. A good practice is to brake firmly just before parking the car after driving in wet conditions, that will help the brakes to dry up. Volvo went from cromate to white zink due to environmental concerns, problem is that white zink does not last very long
5. Brake shields rust, the zinc layer only lasts a few years. Probably not very expensive to replace. If I get new ones I will spray them with wax.. That is by the way recommended on all galvanized parts by corrosion experts
6. Rear wheel-arcs, the area just behind the wheel has no body coat, I have got some small rust spots there. Spray wax or grease..
7. Stabilizer bar links and balljoints fail due corrosion caused by water entering the rubber boots. Solution: seal the edges of the boots with some grease and the balljoints will last twice as long

I think it is essential to lift the car and inspect the chassis carefully once per year. Grease or engine oil effectively stops already developed rust. The disadvantage is that dust and dirt sticks to it..
Spray wax lasts longer but dont apply on rusty surfaces, it may trap water and allow the rust to develop deeper under the surface
Washing with high pressure is effective but be careful, never spray toward wheel bearings or balljoints, water may be enter and cause failures later
Paintwork: Wash away salt immediately, wax often...