I got an iPhone 4 the day after launch, and just recently picked up an iPad.
Instead of unpacking the USB cable that came included w/ the iPad, I just used the one I got with my iPhone 4. They LOOK identical but I'm not sure - both have the shorter dock connecter part (instead of the longer, fatter ones from before).
I noticed the iPhone 4 USB was VERY hard to insert into the iPad firmly... I had to really push and force it. It connected OK, but not very easily. So I went ahead and used the new USB cable that came w/ the iPad, and it fit nice and easy! No force necessary, it just glided into the iPad.
My question is, are the Apple USB cables not interchangeable with other devices? Was I not supposed to plug the iPhone 4 USB cable into the iPad? I really hope I didn't damage my USB port on my iPad.