Did you change any system files, e.g. to remove bloat. You need to be root to do this, and examples include running the bloatware removal script in this forum, using Titanium Backup to freeze things, renaming system files using Root Explorer or similar. Or worse, did you actually delete system files.
If you ran the script, used TB etc, you can manually reverse these steps (if you have a record of what you did!). If you deleted some system files, then you will need to SBF to ensure the OTA update will work.
But as Captain Howdy says, if ALL you did is run Z4root, you should be OK (although we may then ask why did you want root!)