iPhone Simulator location

Simulator: ~/Library/Application Support/iPhone Simulator/

You can browse simulator files from that directory in Mac OS X.

Update for Xcode 4.4: While the iPhone simulator is still in the same place, Apple has included a shortcut to the iPhone Simulator at:

/Applications/Xcode.app/Contents/Applications

Changes since Xcode 4.3.1

Please note that the new version of Xcode is now available on the Mac App Store. Hence all the stuff that used to come with an installer is now packaged into Xcode.app.

Therefore the iOS Simulator binary is located here:

/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/Applications/

The Apps installed in the simulator along with other configuration files are still here:

~/Library/Application Support/iPhone Simulator/

Here is an extract from the current release notes of Xcode 4.3.1

What's new in Xcode 4.3.1

Xcode is now distributed as an application, rather than as an installer. This change enables Xcode to be updated directly from the Mac App Store.