Never. Both the midas and the forktail have a venomous bite, but they tend to hide in their bolt holes whenever my hands are in the tank. I have both, but not in the same tank. I have heard of a few people being bitten by their Midas blennies, but perhaps it's just because they're more popular than forktails that I hear about them more. I would be much more cautious around a rabbitfish than any blenny.
My Midas is bolder and a bit more active, but I've only had the forktail a short time, so it's not really a fair comparison. I recall the Midas blenny took some time to get comfortable in his environment before he came out a lot. My forktail is still in the getting comfy stage. From what I've read, they do become bolder in time and are similar to the Midas in behavior. I'd say either one will bring a lot of personality to your tank.