The Whidbey May CTP documentation describes a new IDE feature called Object Test Bench. It sounds like this allows you to create instances of objects and poke at them in the design environment, without having to create a test project and write code. Looks neat, but either it isn't hooked up yet or I just can't figure out how to work it. Anybody know?
I'm not entirely sure how much I'll end up using this feature, as I've grown accustomed to keeping code explorations in NUnit test suites that I refer back to when I need to. But it seems to be worth a look, anyway.