This is what I learnt so far:
- do not change fonts, colors styles.
- do not try to add cool up to date, buttons, etc - most users just got used to the way it is right now - do not add anything between rank position and title. no additional icons, etc. folks here got used to scanning HN certain way and more white space makes it harder to read
How would my HN bootstrap look like?
- wouldnt touch the outlook and add minimum additionals: after # of comment I would add ajax-driven "follow" for the post and "follow for replies" - in threads were there are hundreds of responses its hard to catch up with whats new (who wrote new reply); I know you can lookup your profile to see comments related to yours, but I find it kind of hard it this way and you have to leave to post screen.
- add highlighters to responses. karma is good and many times interesting folks have high karma (duh!) - I would add highlighters (opt in/out) for high karma users when they type response so when I scroll long thread and am limited with reading time, I could at least see posts coming from high karma users
- social features: would add IRC, follow hacker (notify me when he posts new stuff, or write a comments), but would never add all the fb/twitter crap. imho hn being less popular is better. this community is awesome as it is
- would do it never ending scrolling like you did, BUT also make it as refreshless as possible - would load stuff through ajax, also monitor the hottest subjects and preload theirs comments in hidden div so when you click "comments" it would show up instantly and just added missing comments that took place from the moment of last reload (all reloads would be silent ajax-driven) - this would give you feeling that loading data is extremely damn fast.
This is for a good start. One day I will get there as I want to learn Python or Ruby :)