I do not find people I would expect for some topics and the same people come up for several topics. Is this also factoring in karma? If so, results will be skewed.
The accuracy would be higher, but there are limited number of comments on HN.
Could you elaborate on that?
If you try "postgresql" or something, there are enough people who have discussed it to provide good results. If you type "hnprofile", likely only these comments will show up.