I am a developer and I have been testing all versions of OS X since Leopard. Generally I embrace all new versions of the OS even before it is released to the public. I adopted Snow Leopard before anybody was ready for it. I adopted Lion (even though I didn't like it that much at the beginning) and loved to upgrade to the Mountain Lion long before it became public. I have been testing Mavericks since last June as soon as it became available, but this is the first OS that I have reservations about it. It never clicked-in the way the previous OS's did before. There is an annoying issue that still remains unresolved in 10.9.1; Two finger scroll using Safari, though the problem exist outside of Safari as well. For those who are unfamiliar with the problem, here is a link to a thread that describes the problem in great detail: http://forums.macrumors.com/showthread.php?t=1652376 I have various Macs at home and I have tested all versions of Mavericks from upgrades to virgin installs and the problem exists on all versions. Aside from this annoying problem, there are other negative issues with Mavericks that makes me hesitant to adopt it. Parallels 7 needing upgrade is one of them. Choice of colours in Calendar, particularly not being able to see "today" as clearly as it was on 10.8.x, deletions in Activity Monitor such as the disk space and not being able to select a particular disk to examine the I/O, the implementation of label colours with next to invisible dots as opposed to clearly visible bars is to name a few. So, for the time being, the negatives of Mavericks outweigh the positives of switching from Mountain Lion, despite the fact that Mavericks has substantial advancements under the skin such as the memory and the power management. Up until Mountain Lion the user interface was fluid and flawless. In Mavericks, I feel that they took a step backwards. What is your opinion and how comfortable are you with Mavericks coming from Mountain Lion?