I recently upgraded the ROM on my HTC OneX from ViperX 4.0.3 to ViperX 4.0.6. Being in the IT Infrastructure field from past 12 years, I always value the process of taking backups. Though HTC provides its own Backup App, I still thought of not taking a risk by just trusting HTC. This paid off in a great way.
I initially installed the Online Nandroid Backup App from Google Play and took a Nandroid Backup (This process takes a snapshot of your existing Phone settings along with the Phone Software, so that you can restore your phone to the current state in case of a ROM upgrade failure). I then used Titanium Backup App and took backups of all Apps which had user profile data, viz. WhatsApp Messenger, Viber, Truecaller, etc. I then upgraded the ROM and the HTC Backup App ensured that all Apps and Phone System settings (including the App groupings in App drawer, Desktop icons, etc.) were restored.
Though all the Apps were restored what wasn't restored were the user profile configs. So if I tried to launch WhatsApp Messenger again, the App would treat this as a new install and go through the entire activation process. At this point of time I fired up Titanium Backup again, went to the Restore mode and selected the Apps which I had backed up and restored ONLY the Data and NOT the App. Now when I launched WhatsApp Messenger or say Viber, I would get to see it pre-configured, just like it was before the ROM upgrade.
Another great help which happened taking a backup was restoring my Exchange ActiveSync account along with the Exchange Security Policy. When the HTC Backup App finished restoring System settings and Apps, I started the Stock Mail application which instantly prompted me that Exchange Security Policies need to be applied on the Phone. On selecting Yes the Phone screen kept on blinking and went onto an infinite loop. That is when the Restoration of the Data for the Stock Mail App helped.
But please remember that this process is only for full upgrades which need to perform full wipe. If they are incremental upgrades, don't go through this process.
So next time before you do a full ROM upgrade, do not forget to backup specific Apps on your Phone....