In particular we are developing for Intermec CK30/CK31 running Windows CE. We have an existing C++ project that also targets newer devices (running Windows Mobile 5/6).
The guy who has left this with us, just used to use both environments to develop the one set of source. But I would rather ditch one and develop for all in one environment.
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If you are using different environments with different versions of visual studio, you might want to have a look at the cmake builder.
It is a meta-build program, in that it creates a requested build environment (eg. VS2005 or VS2008) for you. You maintain one set of source code and then choose what IDE/compiler to use to build/modify you code. And each developer can choose a different IDE/compiler.
This would be a good compromise, as you are separating your code from your compiler/IDE, and cmake makes it no effort to drop/revive a target compiler/IDE should you wish to later.
You should be able to use VS2008 for all your development. You'll need to install the platform SDKs for the Intermec and WM versions (WM 4.2 and 5.0 standard should be there by default). VS2010 doesn't yet support Windows Mobile/CE development.