I just (pre) ordered my very own iRig from Amplitude. I am really enthralled by the design that Amplitube has pulled together here. As an occasional bassist and guitar player this looks like a great solution to providing portable amp modeling. I travel a lot and this should be a great device to practice playing. Note that the device won't let you play along with songs on your iPhone since they learned that it created too much latency, although that was the original intention of the design. They are also offering 3 different versions of the iPhone application, one free and two higher levels with additional functionality, including more amp models.
UPDATE (6/8/10): I just saw a twitter post from IK Multimedia that the iRig is scheduled to be released on 6/7/10. (9 days from now).
I've used Amplitude on my studio computer and it's amazing. I'll post a review once I receive the actual unit. Until then, enjoy a couple of youtube videos highlighting the product:
Amplitude iRiq Features
IKMultiMedia YouTube Channel