We use Citrix so I'm somewhat familiar with it and although I have not implemented VS.NET ON citrix I think I can answer your question.
I don't think you'll have a problem with VS.NET in Citrix if you are developing non-web applications. I would imagine that it wouldn't be a whole lot different than running any other application with multiple use instances. One issue might be security and what a developer needs vs. what you'd need to type word docs.
With web applications I'd say it will be close to impossible because of the need for VS to talk to IIS. The web project working directory will be mapped to a single virtual directory and if you could even get it to work you'd end up with people stepping all over each other's toes. And this is not to even mention the impossible task of debugging. As soon as someone hits a breakpoint, they will hijack the IIS execution and stall anyone else trying to run the app.