Open Mind comes to an interesting conclusion - it could work, if the elders actually give the right input. They may be privy to something disturbing about a prospective date/mate that few others might know.
But there are obvious problems with relying on elders, as some responses have already shown. One thing I'll add is that, unless there is something disturbing in the file, the elders often do not know much about a person in regard to what makes him/her a good marriage prospect. For instance, elders may know a brother, but how often do we see instances where brothers put on their best appearance just to impress the elders? Elders often know brothers only in respect to what they see of them at the meetings. Or, they draw conclusions on fitness of character only from jw-related criteria such as hours on a service report or whether a brother shows up to carry a microphone at the meetings. These things do not correlate into what kind of marriage partner a person will be, but it's often the basis for whatever judgments the elders make.