Hello sir,
There are many challenges for migrating an application to the cloud. I feel the following are some important points to consider,
1. Quality of the application : The migration of the app to the cloud should not dilute or eliminate the functionality of the cloud. Moreover this depends on the application.
2. Offline availability : U need to reconsider whether the app is completely for on line use. however, offline cloud computing is also an rising issue!
3. As always security is always a challenge.
4. Availability of the cloud application.(as per the time zones)
5. Lack of administrative privilege : We may get little root access to the migrated application when compared to a normal application.
And there are many more things to consider .. and all that depends upon the type of the application.