In some ways this is similar to Launchrock from the perspective of the poster. However, whether or not it's usually true with most launch pages, when you show people your launch page you are implying that you intend to launch.
The purpose of posting to Launchsky is to get feedback, in the form of interest and comments. One user might post up five ideas (basically visual elevator pitches) and be able to decide from user comments and votes which idea holds the most promise (or which ones don't stand a chance for reasons X, Y).
I used Launchrock the very first time I tried to "bring an idea to the world" and had maybe 40 signups. Mostly friends. If you're just starting out, you have no idea how to bring traffic to your site, create buzz, or do any kind of online marketing at all, so I definitely see value in being able to submit an idea to a community of early adopters and get at least an inkling if this is something worth pursuing.
