According to AppleInsider, the Wi-Fi version of the iPad is still on schedule to arrive April 3rd, but now most accessories won't be arriving until late April, early May.
The article mentions that not only is the keyboard dock delayed until May, but the 10W USB power adapter and iPad soft case could be delayed, too. The iPad dock and dock connector to VGA adapter are still scheduled to arrive with the iPad, and the Apple in-ear headphones with remote and microphone remain unchanged.
I'm sure that there are plenty of iPad case manufacturers jumping for joy right now. With Apple's own version not being available on day one, one would assume that the company will be stocking more than enough competitors to make up for the difference.
The keyboard dock's usefulness will definitely be challenged with it not shipping with the iPad. After all, a few weeks without a keyboard dock could convince many users that it was an unnecessary add-on for their needs.
I still don't understand why Apple doesn't just open up the bluetooth connectivity a bit more and allow for wireless keyboards to play with the iPad. Maybe they will, now that their own keyboard add-on is delayed.
UPDATE: A reader has pointed me to an article where they're claiming that it's a known fact that any Bluetooth-enabled keyboard will work with the iPad. I have not received confirmation of this, but thought it was appropriate to point it out.