> If it doesn't sound compelling enough after the first sentence then you probably need to work on your pitch.
How compelling do these sound...
"Search engine" (Google)
"Computer languages" (MS)
"Directory of stuff on the web" (Yahoo)
"Online store builder" (ViaWeb)
"Computers for ordinary people" (Apple)
"Online photo album" (Flickr)
"Rate pictures of people you don't know" (HotOrNot)
"Blogging" (Blogger)
In many cases... "yet another X". Difference being in execution...