I don't know if it will work for you, but this has worked well for my boyfriend and I.

I said when I moved in I that I can be a bit of a clean freak, and that my expectations might differ from his and I hoped we could work something out. So from the begining I let him know what my expectations are. His response was "I can be a bit of a clutter, but as long as you give me 1 room that I can have my way, I will make an effort on the rest".

And by truth its worked great. We each have our little "area" that can be cluttered (his the study, mine my clothes in a corner of the bedroom), yet the main traffic areas are pretty decent, and it all makes it much easier to hide/clean when company comes.

Guys hate a "bait and switch" by over-tolerating until it becomes too much, or the feeling they have to change 100% to accomidate. Try a compromise? Give him an area he can get messy with that you will accept, in exchance for areas that he must make a better effort to keep clean for your sanity. Once he realizes he doesn't have to completely change who he is to make you happy I think you'll both be sleepin better.

Make it clear that his efforts make you happier, and not just "well its about darn time", because there is no positive feedback there. If anything its a backhanded compliment if that, and thats in no way encouraging. I find my guy will do just about anything if he thinks the reward is worth it.. and ultimately guys want us happy to make them feel successful in the relationship, no? Start little, baby steps, cleanliness is a habit, not a personality trait. Start with having him help you, involve him... make it fun, make it playful.. make him realize that helping you is rewarding to both of you. Granted you can't make people do 180's but change IS possible. Like someone said, people *grow* in relationship, just gotta make sure its in the right direction.

Good luck!