If I have Both Visual Studio 2008 and 2010, do have I have to keep both

I recently downloaded VS 2开发者_JS百科010 trial, the new version is more easy to use. I have VS 2008 installed, If i decide to use VS 2010 in the future, do I still have to keep VS 2008? Is there any compatibility issue with it?

You would need to keep VS2008 installed if you target Windows CE (via Compact Framework, native smart device projects, etc.)

http://msdn.microsoft.com/en-us/library/sa69he4t.aspx

Also if you want to write native applications that run on versions of Windows before XP SP3 and Server 2003 SP2, this is no longer possible with VC++ 2010. The same applies to managed code written for the .NET Framework 4.0, but you can still use Framework 3.5 with VS2010 for projects with managed code only.

And Intellisense for C++/CLI code is gone (MS promises to remedy that in the future, whether a service pack or the next version I cannot say).

If you open a VS 2008 solution or a project in VS 2010 it will be converted to VS 2010 and you will not be able to open it in VS 2008.
If that is not a problem then you don´t have to keep VS 2008, unless you are using a addin or some other third party application with VS 2008 that is not compatible with VS 2010.

Edit:
Look at Ben Voigt´s answer for information for which version have support for different platforms.

VS2010 allows you to specify the target framework that you'd like to develop on. There should be no reason to keep VS2008 installed unless you've become accustom to some handy plugins :)