"You must be level 70 to join my WoW guild, you n00b!"
If this is the attitude that forum members are going to have, claiming that everyone's first post is stupid (and for the record, mine was not), that post count or the time spent at this site is a metric for how worthy an individual post is, then maybe, perhaps, we should do away with the post count and maybe even the date of join on the left side of the page.
Seriously, think about it. If you have no user metrics tagged onto the posts, then everyone's opinions can be judged exactly for what they are, and members could have better discussions because they won't be so focused on post count when writing a response. There also may be a decline in the "report and move on" or "use the search button n00b" comments, which may I add, pretty much do nothing but boost the member's post count.
If there are people (who may I add have been here for less than half the time that I have) thinking that I shouldn't be entitled to post my own threads because my e-penis isn't big enough, then something has gone clearly wrong.
In short, any sort of post count limit to hold back any privileges is a bad idea. Anyone who thinks otherwise is apparently too much of an elitist to see why.