@ OP, depends what you want the feature for really.
Personally I wouldn't use it on my site, I did install a plugin for it though but I quicly removed it as it wasn't doing what I wanted it to do. For some reason since upgrading to VB4 the dumplicate post warning no longer works and I'm getting plagued to death with DP's (not the sexual kind

) I thought the plug in would stop that but it doesn't, it actually makes the site look worse.
For here, I think it's fine though. These boards are very large and you don't want to have the place overly cluttered.