Sometimes you find that the overlays don't reflect the real status of files and/or folders. Usually, hitting the F5 key is enough to make the overlays appear correctly (you might have to wait a few seconds until the cache has fetched the status again).
The treeview on the left side of the explorer is a whole other story. It won't update the overlays, no matter how many times you hit the F5 key. That's a problem with the explorer and outside of TortoiseSVN's reach.
A short explanation:
The treeview always shows the whole explorer tree, including network drives and other namespace extensions. Since these can be very slow (e.g. slow network drives), the explorer tree doesn't ask the overlay extensions for updated overlays all the time. Even if you tell the explorer that a folder has changed and it should update the overlays accordingly, it doesn't do so. It first checks itself if the folder really has changed and only updates the overlays if it thinks the folder really has changed.
Now, since the Subversion status of a folder has nothing to do with the folder itself, the folder itself never really changes (only some file inside the .svn folder, but not the folder itself), explorer therefore doesn't update the overlays.
There are some tricks and workarounds to make the explorer refresh the overlays even on the left treeview, but those are tricks and workarounds, which obviously don't work all the time.
There's one trick that usually works, but it is slow and TortoiseSVN can't use that trick on-the-fly - it just would slow down the system too much. But you can trigger that trick manually by executing the 'cleanup' command on the root of your working copy. After the cleanup command has finished, you have to wait a few seconds for the treeview to update the overlay icons.