flow|state has a great pair of articles that summarize well the problems a web application will face with too many obstacles for new users.
First, in Hurdles at the entrance to a site:
It’s not unusual for a site to position a long sequence of hurdles just inside their entrance. Someone walking in the door might have to clear some or all of these hurdles before they can even try out the site…
The list that follows isn’t much of an exaggeration. So many sites require signup and verification before you can figure out what they do, let alone start playing with it.
With all these hurdles, it’s a small miracle some web-based services end up with any users at all. Each hurdle constitutes an opportunity for the user to leave.
The follow-up article is Easing visitors into a site with anonymous accounts which references PageFlakes and Netvibes as two new sites that let you create a customized page (in other words actually use the product) before ever signing up:
The general idea is that the user will figure out what the product is by using the product itself—not by reading marketing verbiage or sitting through a demo.
I think ESPN’s latest redesign let you make similar changes before creating an account, but in my case those changes were lost once I finally registered. I haven’t tried PageFlakes or Netvibes yet, but if they can smoothly handle the transition from “I’m just trying it” to “sign me up!”, they’ve solved an important problem.