When copying a path by using the the menu commands, if there is any graphic style associated with that path, a duplicate graphic style will be made. We deal with copying hundreds of lines. As a result, we are left with hundreds of graphics styles that are duplicates. This slows the program down by a significant amount. Is there any fix to this? We do use the ALT shortcut when we can, which does not create duplicate graphic styles. But, there are some instances where this cannot be used.
I'm going to take a guess here - if you create a brand new document and do not paste anything into it, but create a path, apply a Graphic Style, then copy and paste that path, you do not see this problem right?
If that is correct, then my guess is that you frequently work with files where some of the content was created in a much older version of Illustrator and you should refer to this knowledge base article to see if it can help: http://kb2.adobe.com/cps/408/kb408008.html