This video shows you what a good couch cleaning can do for your upholstery. I'm not sure if Karcher is still selling this upholstery cleaning machine, but if you like to do your own cleaning this seems like a handy upholstery cleaner. As a professional upholstery cleaner in Tampa FL I can tell you that the results seen in this video are common on synthetic furniture. Microfiber and polyester based fabrics allow for oil build up but with a good couch cleaning will remove the build up pretty easily.
Cleaning cotton and wool based fabrics can be more difficult because natural fibers stain more readily and are less forgiving with accidental spills then synthetic materials. I can't tell in the video what type of material is on this couch but it seams to clean up nicely.
If you plan on doing your own couch cleaning. Plan on it taking about 2-3 hours to clean a couch properly. Even with professional equipment and commercial solutions it still takes me 1.5 hours to clean a 7 foot (3 cushions) couch. Dry times can take up to 4-5 hours depending on how cleaning passes it takes to get the dirt out of cushions. If you're not sure what material is on you couch I don't recommend cleaning it yourself. Instead, have a professional upholstery cleaner take care of it for you.