Gecko,
I think the 25 posts works brilliantly. I remeber being frustrated trying to reach 25 posts as well when I first got here, but it really doesn't take long at all. And I think it serves more than just the purpose it was intended to serve...
In addition to weeding out the bad seeds it also "trains" the new members to post. What I mean is that, it gets a new member (like myself) in the habit of posting rather than being an inactive member.
Ginny and I are good examples of how the 25 post rule actually does work. Even though both of us were frustrated at the rule, for me, it took several days to reach 25 posts, but by then I'd formed the habit of coming here and being an active member. For Ginny, it really only took her a day to reach her 25 posts and so in one day, she made the committment to be here. It is my estimation that she is going to be a great active member or she wouldn't have spent so much time yesterday and today trying to reach her 25 minimum.
Ginny, congratulations on reaching 25 posts! Enjoy your new home in Slytherin (I'm assuming that's where you'll be)
So, the 25 post minimum isn't all bad