In terms of your specific questions:
1) Much of the content I have on my main sites is user generated, this is syndicated using rss feeds. I also add my own material, often rewritten from other sources to which I hold the rights for reuse.

2) On my content heavy sites the front page is essentially a gateway to the rest of the site and so is mainly links to the content in the rest of the site, a typical Dolphin setup. The search engines kinda live on the front page and find the site content from see more the links, tags & categories.

3) As to quality, whilst I am sure that Google et al are working on sorting out well written content or content that has novelty value - adds to the sum of human knowledge - for now the best mark of quality for SE's seems to be the traffic and bounce rate to and from a page. If a page as a load of links, gets traffic and the traffic does not bounce back off the page but stays and visits deeper then a safe assumption is that the content is of acceptable quality for its readership and provides good value for the readers. My Dolphin based site has a bounce rate in the mid 30% range, users hang around for over 14 minutes and read on average 6.5 pages each. I am guessing that Google would not have a problem with seeing this as decent quality content. ;)