You just don't do it any more because of the way Xcode 4's integrated Interface Builder functions.
When you are looking at an Interface Builder view, try clicking the button that looks like a little tuxedo - a variant of Apple's annoying (to me, can't explain why) "assistant" icon. You will get a pane of the corresponding source file zooming in. Control-drag from your object to your source file - presto, IBOutlet or IBAction created!
If your IB files are out of sync with source, either go do the "write class files" step in Xcode 3 before switching to 4, or make all the connections again. There is just no need for "read class files" because the xib and source are intimately connected.
See page 65 of the "XCode 4 Transition Guide" This document is worth reading in full even if you've been developing for years.