The xcode 4 preview just came out today. Has anyone tried it yet? It is safe to use for production release? Would love to use the new compiler.
You might want to read the license. That should tell you enough
I think the thing about not submitting any binaries compiled with prelease software applies here.
So no, for now you'll still have to use the stable / release version of Xcode.
The short answer is no - it is only a developer preview. You have to continue to use Xcode 3.2.x and the current released version of the iOS SDK for production code you want to submit to the App Store.
Please note that Xcode 4 is still under NDA. The one place you can ask Xcode 4 questions without breaking your NDA is on the Apple Developer Forums
No, it's not safe for production builds. In general, you should not use prerelease versions of Xcode for applications built for distribution, and in this case it is specifically warned against.
That said, if all you want it for is the LLVM compiler, you can now use that with the normal 4.0 SDK. LLVM 2.0 that ships with Xcode 4 has some improvements, but you can take advantage of most of the performance boosts by switching to LLVM on Xcode 3.2.x.
Also, Xcode 4 is fully project-compatible with Xcode 3, so you can go back and forth between the two. You can do development and debugging on Xcode 4 to take advantage of the new IDE features, and then switch back to Xcode 3 for final testing and building for App Store submission.
Note for anyone installing this - make sure to read the release notes, and do not check the System Tools or UNIX Tools box during installation (they are unchecked by default) - it will affect your older XCode installation.
Basically, just don't mess with the settings during install - unless you are installing on a whole separate bootable copy of OS X.