In at least one case (reddit), the founders had a great sense of design and yet chose to make the site sparse anyway. This was because as a news site they wanted to emphasize the information on the page and make the site itself fade into the background.
The design of ourdoings.com is relatively subtle, as most picture frames are, but back then it was even uglier than it is now. Nevertheless, people look at what they're interested in.
That said, there are some conventions in recently fashionable web applications that seem to be nothing but fashion. That's less of a UI design thing, and more of a marketing thing. Presumably, there is some sweet spot between total conformism and utter disregard for the contemporary norm that strikes the balance between attention-grabbing and comfort-instilling. Personally, I would say: when in doubt, keep it simple. (That's my personal taste speaking, not any kind of business experience.)
We were in WFP07, and just launched the new site this past weekend...it was designed during the time when we were talking to YC companies every week...I wonder if those discussions bred conformity.