You need to more specific with your enquiries about emmanuel, I don't have time to ramble on for ages about my college so can only really answer specific points. To address those already raised:
Yes it is considered one of the harder colleges to get in to, however this does not affect your chance of getting in to cambridge, since emmanuel end up pooling quite a few students who I think quite often get picked up by other colleges. It's just difficult due to the number of applicants (and hence the standard) I believe. The interviews probably arent any harder than at any other college (obviously I can't be sure, but I severely doubt they make them any harder). and anyway, if you do end up getting in, it makes you feel extra special that you beat off so many other people desperate to get in themselves!
Everyone talks about the ducks because that is one of the most obvious distinguishing features of emmanuel. As Lauren pointed out, we have a pond, and hence we have lots of ducks. It's quite nice to see them around and about; they usually spend their time next to the pond, but can often be found collected in front court, or sometimes waddling through the passageways into new court. When there are ducklings everyone who walks by can't help but go "awwwwwwww" (they're so cute they really are, they just get ugly when they mature).
In reality I don't think the ducks are the main reason why people choose emmanuel, it's just an easy answer to give, there's obviously a hell of a lot more to emmanuel (oldest outdoor swimming pool in europe, the only college that does your laundry for you for free, paddock area so you can actually walk on the grass somewhere in college! etc etc).
Computer science is relatively small at emmanuel, I was a 25% compsci last year, so knew the full compsci's, of which there were 3 I think. Because it's a small subject you tend to have supervisions out side of college for about half of your course, but you get used to travelling all the way to west cambridge for a supervision after a bit.