Everyone seems to start with building their own screenscraper + polling infrastructure (see two cool sites, for example, http://hntrends.com and http://searchyc.com/ ) which seems like a demotivating and fragile obstacle in the way of getting at the problem space where people actually want to experiment.
The SearchYC site (which is great don't get me wrong) has a JSON interface but only for search queries, not the more comprehensive and notification-based system that a definitive API could be.
My comment that there is no API could also be seen as a "gripe" I guess, but I am not really complaining about anything. I love HN and will continue to excessively visit the current website as-is. I also don't even know how PG feels about the issue (i.e., is it "will never happen" or "no time"?).