Every day I have new questions to merit. So, I have activity 238, to the next rank I miss 2. My Merit number is 101 and for the next rank requrement is 250. Will I stay in my full member rank as far as I will not add 149 merits more? Yes? No? Maybe? 
Cases like yours show the challenge with this. I am all for a merit base system, but unless it's fair and attainable, I fear it might have the opposite effect of what it truly wants to achieve. It is darn difficult to gain merits. Unless you are active in the "right" forums it is unlikely that good quality posts will be rewarded at all. Furthermore, although it takes some time to demonstrate sufficient activity, it can take several magnitudes longer to accumulate the right amount of merits. Seeing the numbers above, I have to ask myself how long would it take somebody to accumulate 149 merits? The proportions between activity and merit just seem way out of balance.
Has anyone considered how many good quality posts it takes in general to receive a merit point (on average)? If this turns out more than say 10:1, it would somebody like greeklogos take around 1500 posts just to get to the next level. If the odds would be really this bad (and I don't have much to go on here), the merits could have the effect of destroying the incentive is wants to achieve.