In October 2013 I upgraded both my work Mac running Lion and my home Mac running Snow Leopard to Mavericks. Here's a report of the problems I ran into.
Creating a bootable USB no longer works as easily as it did for Mountain Lion: http://www.oddzuki.com/bootable-os-x-mavericks-usb-flash-drive-9999-error-fix/;
On my home Mac running Snow Leopard I wanted to do a clean install. It turns out this isn't an option in the install process, instead you have to wipe your drive/partition first and then start the installation process;
Admin password problem (didn’t notice lock), only occurred once;
My keyboard lay-out at the login screen somehow got stuck on …continue.