You will need to restore a backup from 2.3.2 (or earlier), as a 2.3.3 backup will not be compatible with pre-2.3.3 firmware. The release notes have some more information, and it actually sounds like one will be automatically restored for you, likely the latest. However, you may want to do it yourself for more control over which backup:
Keep in mind that you will lose any app, device, settings, etc. changes you have made since then--anything stored in the main database.