As traffic increases
...I'll be watching the way comments are used.
Any link entered in the comments in any way (including via trackback) get the rel="nofollow" thing automatically without exception, so the site is of no use to comment spammers. Still, I got one of them. And I always watch conversations that start up in two-week-old posts. Add in one seriously juvenile bit of spew and the thought of allowing only registered folk to comment arises.