Finally upgraded to Ubuntu 11.04 Natty Narwhal. The upgrade went smooth. Download was faster than the actual package update. It is interesting to see the upgrade running while the old system is still usable. I guess they do the actual switch during the reboot. And Ubuntu upgrade takes only one reboot.
But still there was a glitch after the upgrade. It said something that my display mode is not supported and switched it from 1920x1080 to 1024x768. Even if I try to switch it back, the image gets distorted. Then I noticed that Login screen used the right resolution and the same also for the other account on my PC. But when I login to my account the screen switches to 1024x768. Obviously it is some account-specific configuration. After couple of hours searching around I found the guilty file ~/.config/monitors.xml. After deleting it and re-login the screen resolution is back to normal.
Release 10.10 was pretty buggy. As Tom said once there seems to be a tradition of .10 releases being more unstable. I hope that 11.04 sticks to this tradition and is more reliable than the previous one.