Ive completed the first few accounts and transitioned from Yahoo search marketing over to the MSN adcenter and its a very simple process.
In some cases you might not even need to do anything. If you already have a MSN adcenter account and have the same campaigns in both Msn and Yahoo, then there might not be much to do. Yet if you dont have an ad center account, or dont have the same campaigns setup in both Yahoo and MSN, then you will need to do the transition and its pretty simple.
First you need to review the compatibility report and make edits. Then once you start the transition from within your Yahoo account, you will then login to your MSN adcenter account or create a new one. Then its just a matter of going through a series of screens that will pretty much guide you through adding the campaigns that you had in Yahoo into your MSN account. Then you might need to fine tune them somewhat add tweak the bids, titles and descriptions of the ads.
You still need to manage your Yahoo ads though until sometime in late October. Once its complete, then you will just manage your campaigns from within MSN adcenter.