The iPad 2 has only been on sale for a few hours online and already shipping estimates have gone from 3-5 days to 2-3 weeks. Perhaps this isn’t too surprising as analysts believe 15-20% of users of the original iPad will upgrade. This includes me by the way.

Some are calling for 600,000 iPad 2 devices to be sold this weekend in over 10,000 stores from AT&T, Verizon, Wal-Mart and many others.

Perhaps we shouldn’t be too surprised as we know the price of trade-ins on original iPads has been dropping since the announcement of the new device. Mashable has more on whether you should order online or in a store.

My take is if you can’t wait, order one online and stand in line this weekend if you find a store with one in stock.

Update 3/14/11: The delay is now 3-4 weeks according to Apple’s site.