I use two-step authentication for both my GMail and Google Apps accounts as well as dropbox.

Up to now I've been using Google's iOS authenticator app - but this app has issues in iOS7

It forgets accounts when you restart the phone
You can no longer edit the descriptive name for each account so you have no idea which code is which account
Lately it's stopped scanning barcodes too

The first one is of course the most serious.

After some googling I found that there are other TOTP app's out there. I settled on Duo Mobile

After following the third-party accounts page I had both my google accounts and my dropbox account in the app and it's working nicely.