Since the update from Lion:
The Finder intermittently (i.e. several times a day) and inexplicably runs at 100% CPU.
I can’t show the time in the menubar or the systemUIserver process runs at 100% CPU or more. If I want to know what time it is I have to go to the Dashboard.
Every day or two Safari forgets what links are: I click on them and nothing happens. I have to restart the app to get links working again.
The restoration of the good old “Save As…” command turns out to be not a restoration at all, but an incoherent mess of a command.
iCloud is a big bag of hurt. My Photo Stream will no longer update in iPhoto on my Mac, though it updates just fine on iPhone and iPad. Neither do the Reminders sync properly among devices. (I’m back to using Remember the Milk, with its dreadful web UI.) So far iTunes Match is working, though maybe that’s because I had to pay extra for it.
Everyone’s mileage varies, of course, but this is the first time I have seriously considered reverting to an earlier version of the Mac OS since 10.0. I am hoping and praying for a bug-fix update soon (and not 10.8.1, which didn’t do anything to change these problems).