I had a warning that third party software have been disabled. This worried me, since I had few third party apps installed in my PC. Further, I was uneasy about functioning of some drivers after upgrade. The drivers for display card, webcam and wireless card were manually loaded in Karmic Koala. My fears were found to be misplaced. All drivers worked fine. I did not have to tweak any driver files. All thirty party apps worked fine expect VWWare Player. I had to reinstall it. I do not know whether it has anything to do with new version of Ubuntu. However, this also works fine now.
As regards performance improvement of Lucid Lynx, I do not find any visible difference between speeds of Karmic and Lucid. One great performance improvement, I noticed, was in network manager. My previous version had difficulties in connecting to my wireless router. Normally, the signal used to be weak due to location of my PC and vintage PCI wireless card installed in my PC. Now, my PC connects effortlessly even though the signal is still weak. This is a great improvement.
As usual, Ubuntu is becoming more and more stable. Of course, it has added advantage of no viral attack as of now. This may change in due course. My Ubuntu is stable, safe and speedy compared to my Windows.
