HN is the one where I find myself checking several times/day and I constantly have 20+ HN tabs. The pattern is something like this:
1) "Oh, interesting topic!"
2) Open in a tab
3) Read existing comments & the link (I don't always do the latter, admittedly)
4) Come back N hours later, read new comments
5) Repeat #4 over a day or two
6) Close tab unless I haven't read the link yet. If I haven't, then they tend to stick around until I do or send it off into OneTab for ultimate procrastination.