A lot of people who may want to use bitcoins will turn away from it if they are unable to freely use the forums
This.
For an open currency, this is a very closed community.
Five posts is hardly an insurmountable obstacle. Anyone willing to take the time to express themselves in five posts over four hours is welcome. Meanwhile, anyone unwilling to take the time to express themselves in five posts over four hours... well the logical assumption is that they don't want to be part of the community in the first place. As someone who has been reading the forums and learning for a couple of weeks now, I personally prefer this to endless melodramatic/doom and gloom/QQing/troll threads.
Hopefully with this limitation instituted my eyes will get a lot less exercise from all the rolling they had been doing.
P.S. There's 20% of my initiation right there.
Sorry, I didn't make that post very clear. I wasn't addressing the 5 posts currently needed. I think thats a fair requirement. I was addressing the proposed 100 post count suggested by akiyama.