I no longer even bother to notice the last two digits in my total karma, or the last digit in my last-30-days karma.
Which sounds like it makes karma even less useful as feedback for you than for me.
I do skim my user page to take a look at my recent comments' karma scores about once a day or so.
I just found out that a new website feature was implemented 2 days ago. If a comment is voted to -4 or below, it and all replies and downstream comments from it will be hidden from Recent Comments, and further replies in that subthread will incur 5 karma points penalty. The hiding, but not karma penalty, applies retroactively to comments in that subthread posted before the -4 vote.
This seems to be worth a discussion post since most people are probably still voting things to below -3 without knowing the new consequences of doing so.