There's a knowledge base article about how you can split a web project into multiple projects. It's not the simplest process - you have to edit project files by hand - but it would be nice to be able to split certain sections of a web project into their own projects.
Personally, I think this would force me to think much harder about how I want to divide up my projects and make sure that over the long haul, I don’t end up with a bunch of garbled code. I like to try to keep my code segmented, but inevitably, something will come up and the quick and dirty solution (given the timeframe) is to mash something into a spot it doesn't belong. By logically separating out functionality from each other, it would make the temptation (and the time savings) less - and that's a good thing!
Now, to go back and rework a few projects to use this methodology. Or at least test it out. I'm sure there are pitfalls here - like circular references if code is mashed together - but nothing a little refactoring couldn't solve!