In that case it's probably sensible to break it up not only into separate projects but separate solutions too. What bugs me is when relatively small solutions

In that case it's probably sensible to break it up not only into separate projects but separate solutions too. What bugs me is when relatively small solutions are broken up into large numbers of projects. Very often it's done for no reason whatsoever other than aesthetics. They're often divided up "against the grain" too, putting every layer of your application (presentation layer, business layer, repository, domain model, services, interfaces etc) into a separate project, with the result that a single task requires you to make changes to several different projects. The general rule that should be followed here is the Common Closure Principle: classes that change together should be packaged together.