The primary purpose of the front page of a website is to introduce a visitor to the site. The front page should leave a visitor with a clear understanding of the purpose of the site, and of what they would expect to find in the rest of the site.
The secondary purpose of the front page of a website is to provide navigation to allow the visitor to visit the other content contained within. Thirdly, the front page provides news: it's a good place to say what's changed recently; what is interesting at this precise moment in time.
Too many websites get 2, mostly get 3, and totally forget about 1. I'm getting more than a little tired of project websites where I have to scan down the left-hand side to find the link that will take me to the page that finally tells me what the damn project is about.
Exercise for the reader: if you have a website for a project or product, forget everything you know about your project and read the front page. After reading, ask yourself "what do I now know about what I'm doing, and what incentive do I have to click on any of the links that will let me find out more?"
Mmm, tasty, tasty mystery meat navigation.
What drives me _really_ crazy are websites that don't tell you anywhere on their whole damn site. Perhaps I'm supposed to install the bloody thing before finding out.
I particularly liked Cory Doctorow's Eastern Standard Tribe site. Lots about how you could download it; nothing telling you about the book, or why you should bother. It's probably something sci-fi, I suppose, but how can you tell?