Good idea, but I like to up the ante by suggesting a "Compliment" button for every member, so a member can collect number of compliments. So, for example, someone's membership can show something like "Status: Driver, Post: 1234, Compliments: 15".
EDIT: My suggestion, however, can be abused. A friend may compliment one friend who would compliment back, and so on many times over to collect high number of compliments. One way to prevent this is to make it harder to compliment a member, for example, by email confirmation.
For example, I send a compliment to a member, XYZ. An email is sent to me to confirm my compliment. When I confirm it, the compliment is sent to XYZ. Not foolproof, but this extra step can discourage to some degree abuse of this system.
Vbulletin has such add-on that will allow users to "Thanks" a post and the number of "Thanks" received is displayed. Good way to show appreciation for contributors.
There are more add-on for VBulletin than InvisionBoard, like Reputation System where user can add or deduct each other points where users below certain points will automatically fall under moderation where his posts will required review by Admin before posting. Great way for peer moderation that will ease the Forum Admin & Moderator burden but it will make the community points driven.
The abuse could be prevented because it should be able to set to restrict one compliment from one user. Just like the voting system where each user can vote only once.