Not all transfers go smoothly though, and the multiple accounts transfer is what i will definitely avoid as it has lots of bugs. Worst to worst ill manually transfer 1 by 1, but still i expect there to be a couple of accounts that cant be transfered through WHM.
Also i heard that you can do something to the domain's ttl so that there will be minimum data rollback.... Anyone care to explain on it ?
If you have root on both servers, account transfers usually go off quite well. I just did almost a 100 accounts a couple of weeks back without a glitch. Cpanel had improved the code substantially.
As for the TTL, well basically you set it to a low value (example 15 minutes) and wait a day or two for it to propagate. After the account move, you would then want to update the IPs to point at the new server, and within minutes, it should be picked up on most DNS servers and start forwarding traffic to the new server.