I recently moved a 2TB database from Linux, Oracle 11.1 to AIX, Oracle 11.2 using impdp with network_link and parallel options. The data was imported in about two hours and the indexes took another 7 hours. There was no downtime but we kept the users off the system while this was happening.

Here is the command I used on the new server:

Then you can run this to see which parallel process is importing which table:

I had created all the datafiles in the new database and created a db link named olddb beforehand. The servers were on the same local area network and the network was the bottleneck.

You can also read this on my blog.