I occasionally read about people being put off trying the XNA Framework because they don't want to install C# Express, worrying this might somehow interfere with their main Visual Studio installation.
This is madness! C# Express just like totally rocks, dude...
It coexists perfectly with other versions of Visual Studio. I've been running both side by side for a couple of years, while installing and removing various addon packages on a near-daily basis.
It is also just a beautiful piece of software. Clean, light, and fast, it starts up in a fraction the time of its bigger sibling, and I appreciate the less cluttered user interface.
Sure, there are some features missing (I'm a keyboard macro fiend, and I miss my macros), but overall I find myself choosing Express wherever possible. Sometimes less can be more, and I for one will still be using Express out of preference even after uplevel Visual Studio support is released in Game Studio 2.0.