Would you believe this? I use Codewarrior Pro *5* for my Carbon development, and it works.
That nifty little pre-release MSL works just fine, and with the Carbon SDK from Apple, I can take code I wrote in Project Builder and NIB files from Interface Builder and build an OS 9 Package (which works under OS X just fine BTW) of the app with the NIB file that runs the way I would expect.
The graphical quality between a UI generated under OS 9 and OS X is a little different. East/West tab groups don't work right for me under OS 9, and if I sized my tab groups to the size of my window, I would get these odd-looking bevel borders from the tab group right next to the beveled window border. Really odd looking, but I can fix that with a boot into OS X.
Anyways, for OS X-only builds I use Project Builder, which is pretty good for a guy like me who is used to gcc from dual-booting Yellow Dog a couple years back. For the OS 9/X builds I use Codewarrior under OS 9 or Classic, and wind up saving quite a bit of space on the CFM app. My average Mach-O Carbon build for handling just UI is 500+K as Mach-O from PB, but CW will produce a 12K CFM app with the same links.
Does anyone know if CW produces slimmer Mach-O builds than PB as well?