(This has been discussed on the mailing list but I could not find a ticket for it).
If I set my project's 'Kit' to use the LLDB debugger (/usr/bin/lldb) and then try to debug into my application, Creator just freezes.
From looking at the activity monitor, it does not appear that LLDB is even started.
LLDB support really needs to implemented ASAP. Debugging on Mac with GDB via Creator is virtually impossible for non-trivial projects, particularly with Clang-build libraries.
And of the XCode 4.6 developer tools, Apple will drop the LLVM-GCC compatibility frontend entirely along with GDB support. So if this isn't fixed soon, debugging an application through Creator will be impossible on Mac OSX, a tier-one supported platform.
I'm not familiar with QtCreator's source code but I have used LLDB from the command line and I've found it quite intuitive (more so than GDB) so I'm not sure what the hold-up is here.