Add-ins in .NET that you write will work with the version of the CLR you built them with (e.g. 2.0) and they will work on newer CLRs (e.g. 3.0).

When an add-in is installed on a box, it is assumed that the add-in installer will ensure that at least the CLR that it was built with so the add-in will run. So if an add-in was written against CLR 2.0 it should also bootstrap 2.0. That way, with 2.0 installed on the machine, Office will start loading that version (the latest version on the machine) and all add-ins written against all versions through 2.0 will load properly. The bummer for VSTO 1 and VSTO 2 developers was we didn’t make it very easy for you to write those installers–you had to figure out how to bootstrap the CLR you built the Add-in against on your own.

In VSTO 3 the good news is we make the creation of installers that bootstrap the right CLR really easy to create through our new support for ClickOnce. The bad news is that these features work for Excel 2007 and not 2003, so you still have to work through some of the same difficulties if your are doing Excel 2003 development.

Hope this helps–if you need more help or have additional questions, feel free to contact me through my contact form on my blog.

Eric

.NET operate through at least one interop layer and therefore it can be viewed as it has poor performance compared with other development platforms. End users in enterprise do not have any option then to use the .NET based solutions.

Windows Vista is shipped with .NET Framework 3.0 and now when VS 2008 RTM is released which comes with version 3.5 I expect that in the coming SP-1 Vista will also have it.

Today Microsoft only target enterprises with their new versions and tools and nothing in the world will change their focus.

The only real issue is faced by the group of independed (Microsoft depended) developers who try to target all kind of enviroments with their solutions.

The above will be expanded in an upcoming blogpost,

Kind regards,
Dennis