User folder icons replaced by generic folder icons after 10.9 upgrade
Fix:  

Restore the default icons
1. Go to the info view of each folder.
2. Click at the icon in the top left corner
3. Reset the icon via Command ⌘+X

Workaround:
You can copy a folder icon to another folder.

There is a solution to bring the folder icons back:
1. Create a new user
2. Go to the user folder of the new user
3. Select the Documents folder
4. Create a new folder with on an USB stick or at some location that can be accessed from both users (You can also create the folder in /Macintosh HD or however your OS X installation partition is named)
5. Open the Info view of the Documents folder (via Command ⌘+I or via File -> Get Info)
6. Open the Info view of the folder you created
7. Tap on the folder icon displayed in the top left corner, left to the Folder name (It should be surrounded by a blue line)
8. Copy the icon via Command ⌘+C
9. Tap on the folder icon in the Info view of the folder you created and place the icon there via Command ⌘+V
10. Do these steps for all folders in the users directory that have lost their icon
11. Switch back to the user with the missing icons and paste the icons of the folders you created into the folders inside the users directory

I hope that I explained these steps well enough. If you have any questions, just write a comment under this answer

Please notice, that if the folder icons get changed in future versions of OS X (like in Yosemite), you will have to go through these steps again in order to get the new icons