 <p>The only side effect to keep using .NET 2.0 is that you will not have access to features of newer .NET, such as LINQ, Task Parallel Library, etc.</p> <p>See this <a href="http://en.wikipedia.org/wiki/.NET_Framework_version_history" rel="nofollow">Wikipedia Article</a> for a full comparison of framework features by version.</p> <p>Windows 7 already comes with .NET 3.5 built in, so if that is really the earliest OS you intend to target, there is really no need to taget .NET 2.0.</p> <p>If you target .NET 3.5, Windows 7 users can run it with no prerequisite to install .NET 4.0 or higher, but Windows 8 users will need to enable .NET 3.5 (see Scott Chamberlain's answer). So either way, there is a tradeoff.</p>