My iMac is from 2011. Usually I always like to keep my software and OS up to date, but I use SketchUp practically every day (along with Maxwell Render) and so compatibility is a concern. I've been quite content with Mountain Lion so if there were issues with SketchUp running with Mavericks I could wait until things were ironed out.
That said I've been reading reviews of Mavericks and most of the changes are apparently "under the hood" so to speak in terms of efficiency and performance. Thankfully the user interface has been tweaked but not changed (as I understand it) and not as drastically as iOs7 on iPad and iPhone. I'm glad for although my mobile devices do work a bit better I don't care for the look of the iOs7 user interface with its simplistic and cartoony looking icons and such. Still, I am getting used to it.