I'm generally a late adopter when it comes to OS X versions, despite being very technical and generally excited about new features. I have several Macs that I use (work machine + multiple machines at home). I've got one machine that I'm running Mavericks on to test it out, but all the machines that I do any real work on are staying on Mountain Lion for the time being, including my wife's MBP.
The MBP I installed Mavericks has been rendered unusably slow after the upgrade, and I'm pretty sure I'm going to downgrade to Mountain Lion and maybe even dual-boot Linux to allow for a more lean environment. Granted, it is a pre-unibody early-08 15", with only 4GB RAM, and a 5400 RPM HDD, but it was running ML fine. Now it often takes minutes to startup apps. I'm waiting all the time for it to complete tasks so much that I can never actually accomplish anything on this laptop.
Usually my work machine is the last to get an OS X update out of all my machines. One of my coworkers upgraded to Mavericks on day one and he keeps telling me about various bugs he's experiencing (often with 3rd party software). I really could use the new multi-monitor features (using 4 displays right now), but ML works so well I don't want to mess with it.
For my home machines, staying on ML means I can't upgrade FCP X or Aperture any further, but that's ok, I'm happy with the versions I'm stuck at. I might buy a new Mac later this year which will force me into whatever the latest OS X is.
I started using Macs at 10.4. Leopard (10.5) and Mountain Lion (10.8) were the only releases that I think were worth upgrading when they were first released, and the rest needed bugs shaken out. Leopard because it was just so much better feature-wise, and I didn't have any issues with it (though it was a PPC machine that I upgraded). Mountain Lion because it was basically just Lion with bug fixes and some nice new apps, so not as much potential for breakage. Even Snow Leopard, now considered rock solid, was buggy for me and I ended up downgrading back to Leopard until the bugs were shaken out.
What's annoying is that I now periodically get notifications to upgrade to Mavericks in ML. Maybe there is a way to turn those off?