On Mac there are quite a few shortcuts in System Prefs that seem to be in conflict. You should disable them there.
Sorry, I should have mentioned. Yes, I'm on a Mac (OS 10.8.4).
If that's the case, that these are system preferences, is this something that's only a problem with the CC versions? Like I said, the exact same quick keys work fine on CS6.
Yes, it seems only to affect CC.
I have InDesign CC on a Mac with Mac OS X 10.8.4. I have no problem with the Save As shortcut (Cmd+Shift+S). While Peter is right, there are a couple shortcuts like Cmd+Shift+L that are taken over by the OS by default (but can be changed in System Preferences > Keyboard > Keyboard Shortcuts), that is not one of them.
I'd suggest you probably have some other utility or application taking over those shortcuts. So you might turn off any startup applications that could be conflicting.
If you'd like to list other shortcuts that don't work for you, I'll be happy to try them out for you.
Thanks very much for you help. I was able to fix Save As, but the another one that I know of for certain, Edit Original (CMD + OPT + Shift + D) I can't seem to find. I'm also looking through my start-up applications to see if the trouble is indeed there.
This is a symptom of InDesign believing that the keyboard shortcut is allocated to a menuitem within the InDesign menu, most likely within the Services menu.
Similar behavior is seen for Cmd-Shift-L, which is InDesign's shortcut for left alignment, but by default recent versions of Mac OS X assign it to Search With Google, though it should only work when text is selected. Sometimes the OS beats out InDesign and sometimes it doesn't. It's clearly a bug in how InDesign handles its keyboard shortcut interface with the OS as a result of Cocoaization, and I understand InDesign Engineering spent some time trying to make it work and did not succeed.
Perhaps you can look in the Services menu for a clue, though its contents sometimes changes dynamically, so that may not work so well.
(hrmm; I see others have covered the above while I was doing other things. oops.)
With respect to Edit Original, are you aware that you can invoke that by option-doubleclicking? Not the same, but I find it more convenient.