Technically My site consists of User Profile and personal site with content. (Refer the following article for more detailed explanation: Introduction to My site)
MM allows you to move site with content by does not move user profile. So, you need to take care about profile creation on target farm.
03-07 migration:
1. Pre-create user profile on target farm. You can do it by importing User Profiles or creating a profile manually (Shared Services Administration > User Profile and Properties > Add user profile)
2. A user whose personal site you are migrating should have no existing My Sites in MOSS 2007 (If the personal site already exists Site settings will not be migrated).
3. Migrate source user site collection into a new site collection with appropriate name.
Note: When specify name of target site collection it should correspond to “Site Naming Format” option (you could check it in "Shared Services Administration > My Site Settings > Site Naming Format")
Example:
On source farm you have "User name" format:
But you want to change it to "Domain and user name" on target farm to resolve conflicts:
So, you should specify appropriate leaf name for target site collection when migrating site collection for "k8\user1" user:
07-07 migration:
The same steps are right for 07-07 migration but in some cases SharePoint automatically creates user profiles on target site. So, perform a test migration without pre-creating user profile and try to access target site. If you receive the “Site Collection already exists” error that means you need to create profile manually.