I have no problem getting them to clean the floor, but now I have a big smudge of dirt on the desk top. If I try to drop someone on it all they do is surf the web or work on career or something. How do I get the desk clean?

Threaten them!!!!LOL
Ooh that sounds hard..... keep trying to drop them on differetn places near it. If that doesn't work I don't know what you should do.

Hire a maid when you get the opportunity.

If it is ON the desk, you may not be able to clean it. It is the same if a sock or wrapper appears on the desk. You can't do anything about it (unless the maid event comes along, not sure if that takes care of it or not). Sometimes these go away on their own over time, sometimes not.