What reasons are there for continuing to run Visual Studio 2005 when 2008 is available?
I work on a project where the environment is dictated to be Visual Studio 2005. Are there good technical reasons for this? Can I use Visual Studio 2008 and build an app that is 100% indistinguishable from the same app build with Visual Studio 2005?
Not really, the new version of Visual Studio has the compilers for the new language versions and all the libraries for .NET 3.5. Since they all target the 2.0 CLR and Visual Studio 2008 allows you to target previous versions of the framework I don't see any reason to stick with 2005.
We are currently migrating from 2005 to 2008. If you open and save a project while in VS2008, you will not be able to open that solution/project in VS2005 (at least we couldn't find a way easily). If the rest of your team is still in 2005, you should stay there. You CAN, however set up a project in 2008 and keep it compatible with 2005... as long as everyone opening it is using 2008. You keep the .NET version at 2.5, and don't convert most of the stuff that it wants you to convert.
The only time you CAN'T migrate to 2008 is if you are using a report project and SQL Server 2005. VS2008 will only let you integrate a report project with SQL Server 2008. What did we do?
We migrated to 2008 and all the Team Server stuff, except for the database and reporting. Those we kept on 2005, and so I end up having to open both versions on a daily basis... but that's why they pay me the (somewhat??) big bucks!
I think there are two questions here
Generally speaking the answer is yes. I do this frequently with several internal and external hobby projects with great success. You may encounter an odd ball tooling issue but so far none has cropped up for me.
The best reason I can think of is a large developer environment. Once you make the switch to using VS2008, it will upgrade all of the projects in your solution to the new format. This will no longer be usable for anyone using VS2005. They will be forced to upgrade or maintain parrallel versions of the project file. In general, I find it's best to upgrade in groups rather than individuals.
The obvious answer is: No license for Visual Studio 2008.
My company is "saving money" but not upgrading...
One reason might be interaction with existing products. I write code for AutoCAD in C#. They (Autodesk) "officially" support VS 2005 but I've been using 2008 since...well 2008.