This type of board is based off of 2channel, pronounced "Ni-channeru", the largest Internet forum in the world (20 times larger than the biggest American forum). Shiichan is somewhat different from the 2ch look, but they still use the same system. Kareha is very closely modelled on 2ch.
On the other hand, you're interested in starting a forum on some topic of your interest, and allowing anyone to post, then 2ch-type is infinitely better than PhpBB, Invision, or vBulletin. I'm going to refer to these as "old-type forum software"; I'm not pretending to be unbiased.
Trolls are not out to protect their own reputation. They seek to destroy other peoples' "reputation" ... Fora with only registered accounts are like a garden full of flowers of vanity a troll would just love to pick.
If there is a user ID attached to a user, a discussion tends to become a criticizing game. On the other hand, under the anonymous system, even though your opinion/information is criticized, you don't know with whom to be upset. Also with a user ID, those who participate in the site for a long time tend to have authority, and it becomes difficult for a user to disagree with them. Under a perfectly anonymous system, you can say, "it's boring," if it is actually boring. All information is treated equally; only an accurate argument will work.
Problems with 2ch-type forums often come along the lines of "people will be more likely to insult, flame, and troll if they're anonymous". This may be true... but people are already pseudonymous on most forums. The drama and hatred you see on pseudonymous forums is as bad as it gets; with anonymity, you'll probably be better off because of the convenience. Either way you will need a dedicated team of moderators to police the board for trolling and nonsense.
Spam is another issue. Since 2004 when this essay was written, message board spam has become increasingly prevalent on all anonymous forums. However, on old-style forums spammers often register fake accounts and happily suck in users to their profile websites without posting. If you are experiencing spam that gets around your local filters, I have found that extremely simple tests, such as a drop-down box asking whether you are a human (Yes? No? Maybe?) often cut it off entirely.
If you can't or don't want to force people to pay or use their real names, at least give a swing at bucking the establishment and trying out a totally anonymous forum.