So I decided to do the upgrade as well (keeping my original 12GB disk and adding a 48GB disk). The best price I found was with Outpost.com (around $430), which claimed 3-5 day availability, vs. much longer lead times elsewhere.

Guess what arrived in today's e-mail?

Dear DAN :

Thank you for your order! We apologize but the item(s) you
ordered is currently out of stock and we are unable to provide a
definite ship date at this time. However, we continually receive
new merchandise in our warehouse and we hope to fulfill your
order within the next thirty days or sooner if possible.

Brilliant, huh?