Mac OS X 10.8 and beyond
I've been using Mac OS X since Tiger, 10.4 and I have used every OS update since then. Currently using 10.7.2 and while looking back on all the updates, I only remember noticing a real change from Tiger to Leopard and it got me wondering about how Apple will design the future versions of Mac OS X.
Pictures in order from Mac OS X 10.4 to the latest 10.7
As you can see in the past 4 updates, the dock and menu bar changes a lot from 10.4 to 10.5 with some small updates from 10.5, to 10.6 to 10.7. Tiger to Leopard gave a lot of features that I can't imagine living without, like Quick Look, Stacks, and Spaces. Snow Leopard was mostly a speed boost and some very small enhancements.
When I think about the future of Mac OS X, I think a lot about what Lion gave us compared to Snow Leopard. Lion basically turned the Mac OS into a version of iOS. Steve Jobs even said that they are taking their OS ideas "back to the Mac". With the scroll bars looking just like iOS and the Launchpad app which displays your apps the same way they display apps on the iPad. Most of the changes in Lion were not wanted by most people. I don't think I know anyone who uses Launchpad. I can only speak for myself but I'm sure that most people out there want a computer OS to be a computer OS, not a upscaled mobile OS.
I honestly see Apple watering down Mac OS X to be very similar to iOS. They basically destroyed the file system by making All My Files the default view in the Finder in Lion, which displays all of your files in one massive, unorganized place, leaving you no real option to control it. I also hope Apple avoids adding more of these realistic designs like they did with the iCal and Address Book app.
For Mac 10.8, I am hoping for a real massive change. It seems long overdue since all we got for the last few updates were small enhancements. I just hope they don't turn Mac OS X into larger version of iOS but if Lion's trend continues, that's probably what's going to happen.