I don't understand versioning schema. If FX3.0 is only assembly addon, why it is not FX2.5 and LINQ (C# 3.0) version is not 3.0?
although .NET 2.0 is supposed to run .NET 1.0/1.1 apps, not all apps run. Therefore, parallel installs of 1.1 and 2.0 are required. Now, will Vista include .NET Framework 1.1 too?
Why don't you rename the upcoming FX 3.0 to something a little less confusing, such as FX 2.5 or so? That way the next version, with LINQ, will be 3.0, and will line up with C# 3.0 langauge specifications.