Some of my most common issues on my mac (these are things which used to work, but don't work as well anymore):
Spotlight: This has become extremely unreliable (and ridiculously slow) for me. More often than not, it won;t return results, except for an icon for the topmost result which flashes in the search bar for an instant after I hit a key. If I hit enter while that icon is visible, spotlight will open the app/document.
Data Detectors: What happened to these? I used to love them, but they never seem to work correctly for me anymore.
Safari Autofill: Why can't Safari simply autofill my email address like it used to? Why does it have to show me the opaque contact box, where I'm not sure which email it will autofill for me.
Time Machine: Hasn't worked for me in years.
Calendar: I was a ridiculously heavy user of iCal in the mid to late 2000s. Can't use it anymore. I'm not sure what specifically went wrong with it (just seems a lot more clunky). It used to be far more keyboard friendly (I liked Apple Mac apps when every app had a default layout with the side bar, that showed my organization hierarchy at a glance.)
Contacts: To be fair, this (and Address Book) has always been an unholy skeumorphic mess.
Expose: After years of making Expose unusable, starting with Lion, it's actually back to being pretty good now (now that it works closer to what it did in Tiger).
Dashboard: I was one of the few that actually used dashboard. I wish Apple would just kill it instead of what they are doing to it right now.
Dock: I think the Dock has gotten much better over the years, but I think the Windows start bar is superior at the moment.
Force Quit: Why don't my apps force quit like they used to? Force quit used to be extremely reliable, but now it doesn't seem to actually do a force quit at all.
iWork: Haven't dared to go back to iWork since the refresh. Pre-refresh I loved Pages and Keynote. I happened to use Keynote to present a ppt a year ago, and while the conversion was pretty good, the presenter mode was extremely gimped and uncustomizable. I may be misremembering, but I think it used to be far more customizable in terms of being able to pick the info to display on the presenter screen, etc. Numbers was always terrible, so I'm not even considering that.
iTunes: Do I really need to say anything?
QT Player: I think it's improved, but I'd switched to VLC way back.
Quick Look: The switch in the QT engine means the vast majority of my videos don't quick look any more (I think it was Perian that made them work). Maybe I need to search the net again, to see if there are more plugins for this.
Finder: Still as clumsy as ever for file management, but seems to be better at parallelizing tasks. However, file/folder metadata takes way too long to load. It used to be a lot better (I remember I used to have the inspector window in always open mode. I wouldn't dare to do that anymore).
Bah, that was way too long...once I started, couldn't stop, and I can probably go on for much longer. (I'm one of those guys whose 2nd favorite part about an OSX release, after the Siracusa review, would be the Macrumors "Little things" thread).
Spotlight: This has become extremely unreliable (and ridiculously slow) for me. More often than not, it won;t return results, except for an icon for the topmost result which flashes in the search bar for an instant after I hit a key. If I hit enter while that icon is visible, spotlight will open the app/document.
Data Detectors: What happened to these? I used to love them, but they never seem to work correctly for me anymore.
Safari Autofill: Why can't Safari simply autofill my email address like it used to? Why does it have to show me the opaque contact box, where I'm not sure which email it will autofill for me.
Time Machine: Hasn't worked for me in years.
Calendar: I was a ridiculously heavy user of iCal in the mid to late 2000s. Can't use it anymore. I'm not sure what specifically went wrong with it (just seems a lot more clunky). It used to be far more keyboard friendly (I liked Apple Mac apps when every app had a default layout with the side bar, that showed my organization hierarchy at a glance.)
Contacts: To be fair, this (and Address Book) has always been an unholy skeumorphic mess.
Expose: After years of making Expose unusable, starting with Lion, it's actually back to being pretty good now (now that it works closer to what it did in Tiger).
Dashboard: I was one of the few that actually used dashboard. I wish Apple would just kill it instead of what they are doing to it right now.
Dock: I think the Dock has gotten much better over the years, but I think the Windows start bar is superior at the moment.
Force Quit: Why don't my apps force quit like they used to? Force quit used to be extremely reliable, but now it doesn't seem to actually do a force quit at all.
iWork: Haven't dared to go back to iWork since the refresh. Pre-refresh I loved Pages and Keynote. I happened to use Keynote to present a ppt a year ago, and while the conversion was pretty good, the presenter mode was extremely gimped and uncustomizable. I may be misremembering, but I think it used to be far more customizable in terms of being able to pick the info to display on the presenter screen, etc. Numbers was always terrible, so I'm not even considering that.
iTunes: Do I really need to say anything?
QT Player: I think it's improved, but I'd switched to VLC way back.
Quick Look: The switch in the QT engine means the vast majority of my videos don't quick look any more (I think it was Perian that made them work). Maybe I need to search the net again, to see if there are more plugins for this.
Finder: Still as clumsy as ever for file management, but seems to be better at parallelizing tasks. However, file/folder metadata takes way too long to load. It used to be a lot better (I remember I used to have the inspector window in always open mode. I wouldn't dare to do that anymore).
Bah, that was way too long...once I started, couldn't stop, and I can probably go on for much longer. (I'm one of those guys whose 2nd favorite part about an OSX release, after the Siracusa review, would be the Macrumors "Little things" thread).