If you can find any other folders with the same icons -- say, in another user's home directory, which you should be able to see if you're an administrator -- you can do this:
1. Select the folder with the icon in the Finder.
2. Press Cmd-I (for Get Info)
3. Click on the icon in the upper-left of the Info panel. It should grow a blue halo.
4. Press Cmd-C (for Copy).
5. Click on the folder that lost its icon in the Finder, press Cmd-I.
6. Click on its (generic) icon in the Info panel, and press Cmd-V (for paste).
That's assuming you can find folders with their icons intact. Worse comes to worse, create a new user just for this purpose and delete 'em when you're done.
Out of curiosity, what sort of updating were you doing? Losing the icons on these folders means that they've lost their 'resource forks' where such info is stored; usually this is a sign of a buggy or non-Mac program manipulating the folders.
Update: whoops, I could've sworn Administrators could view others' files with a password. I appear to be incorrect. Let me see if I can come up with another way.