I'd prefer not to install the whole iOS SDK with Xcode, just the gcc toolchain for my own console applications and school work. I know for the old Xcode installs it was possible to customize the install and deselect it, but I'm not sure how the Mac App Store handles it and I'd like to know before I buy it and try to install it. The iOS SDK is a good 4-5 gigs of overhead I have no need for, and with an SSD I'm trying to save space wherever I can.
Don't accept this answer without vetting it further first, but I think I noticed something during my install.
I think that you don't get any SDKs as part of the XCode 4 install. It was only after I installed XCode 4 and launched it, that the project window showed a download in progress. Clicking it gave me the option of downloading: OSX 10.6 SDK, Legacy OSX SDK, iOS SDK, and something else that I don't remember at the moment. Perhaps extended documentation.
So, the XCode install itself is still very heavy. What with XCode visually, all it's associated applications and libraries, Clang/LLVM/LLDB, profiling tools, and everything.
But, the SDKs themself? I don't think it comes automatically. I can't seem to figure out how to get back to choose the other SDKs to download, so I'm not 100% sure in this.
Xcode 4 packages could be customise if you use the MPKG installer, this article by Jones Lee walks through the steps needed: Howto fix App Store Xcode 4 95% installation freeze AND customize install template to exclude iOS SDK
If you only need GCC, the OSX GCC Installer project has pre-built binaries.