Some years ago there were sites with hundreds of links on homepage as 500words [dot] com. Are they become harmful to the PageRank?
Yes. if you do this google will look at it as a link farming site and your page rank will be effected.
Yes probably especially if it looks unnatural and irrelevant. Like what robby said it will more likely to look like a link farm.
As others have said, this type of thing would not be a positive at this day in age. Kinda reminds me of the Million Dollar Homepage. Don't think I'd want any of my links on that kind of website at this day in age!
For me it depends if you traffic exchange or traffic website no need to look for google some of them content is links so i think,,,but like for blogs its not a good idea to farm links..