just to have thrown my two cents in where it's not needed, a rank based on the number of posts, will always be sort of silly. do we even really need the ranks at all? they're of little to no importance/use, aside from knowing who's a mod, and who's not, and that's posted in every forum, anyway.
we're all members, no matter how many posts we've made, and as far as being a senior member is concerned, a senior member is someone who's been around long enough to start answering more questions than they ask, has been in a few good discussions, and has had the good sense to stay out of a few bad ones.
just my opinion