Here are a few gotcha's that I personally came across both in the forums and migrations I've done from IIS6 to IIS7. A lot of the confusion I see in the forums is Classic ASP and 'native' applications using COM+ trying to move to IIS 7. A classic ASP.NET 1.1 and 2.0 applications should migrate with little or no issues, that is my experience. You'll need to install .NET 1.1 on Windows Server 2008. The biggest change is to try Integrated Application Pools first, then switch to classic mode. That is probably the biggest recommendation to think about in your migration.

I was involved in migrating a few sites recently with popular content engines. We used the migration tool MSDeploy provided by MS, the one thing that we needed to adjust was the Anonymous Authentication module. We had to adjust so the virtual directory inherited the application pool user account instead of IUSR. I highly recommend using the deployment tool. The one item that IIS 7 manager doesn't match up to IIS 6 is SSL certificate management. It seems more mature in IIS 6 manager IMO.