I am maintaining a VB6 application and we are studying how to migrate to .Net We are considering doing this gradually by implementing new features in COM visible .Net classes and migrating existing functionality slowly. I found some instructive 'Hello World' examples about how to do this and it works fine with our App. But how is the real world behaviour of these hybrid applications? Are they stable, maintainable? Particular of our program is that more users on the same computer will use it by switching user accounts.
EDIT: The VB6 app reads data from a USB connection and stores it in an Access database. The user can call up various views on the data. The data is cached in a hardware device, so interuptions in the reading of it are not fatal.
EDIT 4th Oct 2015: Time for a follow up: We still are in the process of replacing the existing VB6 code step by step to .Net. First we took on the data access routines, then the bussiness logic and currently one form after another is converted to WPF. We indeed ended up rewriting every piece of code we converted (in VB.Net), but we could do so slowly and on the same time improving functionality. The hybrid application survived the transition to Windows 8, 8.1 and 10.
EDIT 9th March 2018: We will release the fully converted code next Month. The hybrid application will be supported for at least a year longer. It is showing mainly problems on high resolution screens, but working fine otherwise. To be honest, we have more support headaches due to corrupt .Net Framework installations and corrupt installations of dependencies (SQL Server LocalDb among them) than we have compatibility issues with the VB6 code base...