Protip: use pixlr.com - it's free and requires no installation!
I made a quick mockup. Is this what you had in mind? (Warning: not a design person) http://i.imm.io/jQMl.png
Such a thing might be useful. Don't know how much an auto-updating feed would impact the very non-live vibe I get from HN, but it'd change post distributions and such for sure. The feature I'd personally love to see is the ability to collapse chains of comments without using an external script. :)
