Are there any known issues around how many "pages" are in an ASP.NET project?
Does the size of the DLL created by the project matter at all?
My existing project is about 150 pages and the DLL is only around 3MB but it has increased from about 50 pages and 0.5 MB recently
I haven't run into any issues with sites up to hundreds of pages in size. How big of a site are we talking about? Are there built-in redundancies between pages which can be resolved by having a single page take parameters?
Often times it makes sense to break down subsections of a larger site or project into multiple ASP.NET web projects. This makes the site way more modular. Additionally, if you have common controls that are used throughout the site that often is cause for a project that has just those controls.
To address the question directly, however, I've managed projects that have many, many pages and have had no issue... aside from it becoming "fun" to browser through and develop against.
Technically, you can have hundereds (I'd venture to say thousands) of 'pages' in a web application project.
What Russell said though, to break it into modules, would potentially make it easier to maintain.
Is there a limit? No. Should you organize your project so that it's easier to manage? Yes.
There aren't concerns unless you are trying to debug it (or turn off batch compilation). Or if you have a bunch of folders. Each folder will have one DLL for all the files with batch turned on. So if you break things up into a bunch of folders, that could cause fragmentation problems of the processes memory. Otherwise, no issues for lots of pages.
Scott Hanselman got on the subject two years ago.
The absolute limit is your system memory. The bigger the project the more memory it will use.
Surely you can stay in a [50-200] projects in a solution.
If you find your Visual Studio taking more than memory than expected start thinking about breaking your projects up.
In my opinion the best thing to do is to make the project size a design requirement.
EDIT : I'm not really answering to your question. To make it clear. The more elements (Pages, projects, image, references, etc.) you have in your VS2003, VS2005 or VS2008 solution the more Visual Studio will take on memory.