I found alot of conflicting info on the topic...
It appears in September of 2010 they did change it, but I think it is only enforced and it is almost even worded as if you just cannot elicit the content of the review...
But It seems to be sort of a grey area as alot still do it and flourish (much like everything else in Google)
I have never personally tried this incentive strategy myself but Have done the citation route many times and seen EXTREMELY good results.
And in my look around incetivizing increased reviews by over 100% (of course) so this may have been why they stopped it, as those with the most money could have the most reviews causing an unfair advantage (but isn't that sort of true in everything?)
Just in my personal opinion since I am not a lawyer nor do i work for Google
Incentive's for reviews are good for all as long as you are not incentivizing the content
1. Customer -
Get the chance to either come back and enjoy another meal/service or If they had a bad time the owner gets to try to make it right...
2. Perspective Customer -
They get to learn about the experience and see the transpareny of the owner either rectifying or not. (of course i understand some clients/customers are unreasonable, but hey it is a part of being in business
3. Business
They get the Benefits in both Word of Mouth and Search Engine Marketing plsu the chance of repeat business OR the chance to right a wrong therefore helping brand image.
It also entices the business owner to strive to be better to make sure they do not incentive themselves into a bad review
But hey this could get you in trouble, but their are lots of risks taken every day in business, must weigh the ROI potential.
w00t!