The Upgrade from OSX Lion to OSX Mavericks took quite a while (about 1 hour and 30 minutes). The installation got stuck towards the end in: “Less than a minute” for quite a while (it must have been more than 10-15 minutes).
I was tempted to hit the shutdown button , as I thought the installation process seemingly froze. Be patient!! Less than a minute, can be actually up to 20 minutes!
Luckily after quite a while the system rebooted, prompted me with the apple screen for 3-5 minutes and then started a post installation configuration that lasted a good 7-10 minutes.
Apparently Avast free that I was using is not compatible with Mavericks. I was prompted after the reboot that Mavericks placed it under the incompatible programs and I had to uninstall it (using the Avast GUI menu).
Update: It looks like there’s also an incompatibility if you are using VirtualBox on the new Mavericks OSX as described here: ttp://kyriakos.anastasakis.net/?p=418