The amount to which the program is object oriented has an inverse relation to:
1. the number of arguments passed in message calls
2. The number of instance variables in the objects
I tend to use "7 +/- 2" rule. If I have 5 or less instance variables in my object, then everything is cool. I'm even OK with 7, but 9 is on the cusp of too many. The reason why is because too many instance variables is not only a code smell, but your object is getting away from having one responsbility and needs to be broken up.
Arguments are little bit more restrictive. I try to keep them below 5. Otherwise, you're writing big methods and well, your methods should do one thing and nothing more.
Of course, the rule above is excellent, as is the "DRY, Shy, and Tell The Other Guy" rule from the Pragmatic Programmers. They are just some things that I strive for when programming.