Have a look at the following layouts for some well known services:
They all look SUPERB. It's obvious that these guys have now invested tons of time and money on making their landing pages (and their layout/UI as a whole) look extremelly nice.
A small team of programmers though (or a solo-superman) may not be in a position to create such a perfectly looking layout/UI nor be able to hire a capable graphic designer right now to do the "skinning" of the app.
So the question is, should such team launch early with a mediocre design? Or should it wait and launch when the UI looks "perfect"? Is there a possibility that the mediocre aesthetics will do more damage than waiting for a couple of months?