for VS 2005 is there a max number of projects that will cause performance issues. We have now up to 25 projects and growing. Should we making these binary referenced or are we breaking out our application logic into too many different projects. Seems to start to be a big performance issue lately.
Having too many DLL files can cost you at run-time so I would recommend that you try to minimize the amount of projects. Creating several solutions is also an option but try to make the solutions independent of each other so that you don't have to debug and implement new features across several solutions - that can be cumbersome.
Take a look at this article: Project anti-pattern: Many projects in a Visual Studio Solution File.