Yehoo!!! Successfully upgraded to Intrepid Ibex. It was online upgrade with "update-manager" which though took lot of time than a clean installation (Yes I also tried a clean installation on friend's laptop :D ) but this saved me from re-installation of additional softwares that were already installed and got upgraded.
During installation, at "Getting new packages" stage, I even canceled the process and it resumed from that point when I restarted the upgrade process. It also showed me the conflicing configuration files like vimrc with nice diff, which helped me to keep my old settings. It then cleaned-up temporary files, rebooted and even my all Mac settings came back without any problem. I just needed to reinstall AWN (Avant window navigator) because I was using it from some other latest repository. The only visible change is new fast-user-switch-applet which appears at right side of top panel and it has options to change pidgin status.
So far it looks good. Will let you know if I catch any problem so stay tunned.