I remain skeptical of a system that rewards quantity over quality. One can argue that posts must have some level of quality to get rated positively, but even a blind squirrel finds a nut once in a while. If one were to make 1000 posts, of which 50 were good and the rest were absolute rubbish, that person would end up with an overall rating better than another who makes 30 top-notch posts without any duds.
I have a feeling this will lead to more people trolling the help forums, responding with 3-5 word answers, or repeating answers others have already given, or saying something like "I agree," just to give themselves a chance at getting a higher rating. There's no system of checks and balances.
The old rating system needed to be changed, and this current system is probably a slight upgrade. But there still needs to be some way to keep the frivolous posts at bay. If you don't want to have a negative rating as an option, why not show the average rating per post instead of a cumulative number?
In the example I mentioned in the first paragraph, the person with 1000 points could get +2 on his 50 good posts for a rating of 100. The person with 30 great posts could get +3 on each for a rating of 90. With a system that shows the average rating, the first person would register at .1 while the second would sit at 3, which is a more accurate assessment of each poster's overall contribution. Hell, go with both: total rating AND average rating. Just don't make quantity the only thing that gets rewarded!