No reports of Pink Screens of Death this time, but Apple has released the fourth version of their SDK (5A258f), which weighs in at a beefy 1.15GB (200+MB for firmware) and according to TAUW (via Apple Developer Connection) sports:

Xcode IDE, iPhone simulator with Open GL ES support, Interface Builder, Instruments, frameworks and samples, compilers, and Shark analysis tool.

In addition, code-signing is now enforced, Audio Toolbox was big-upped, NSXML parser was introduced, fonts were given some pro love, and -- teasingly -- the UIApplication delegate class is now rumored to have Springboard Icon badging and some way to get and release "active status". TAUW speculates this may allow some form of background functionality for Apps! (Wishful thinking?)

Go get 'em developers. Especially you deep-code-digging developers who find all sorts of goodies hidden in the strings.