Front of the Super's Ranger has one, awesome for front diffs! Love it.
Is it a true locker, or is it a limited slip unit?
I imagine that a true locker would be overkill for a front axle on a vehicle that doesn't see much in the way of hardcore off-roading, but converting an open to limited slip is appealing. My old Scout had limited slip front and rear and would go almost anywhere
And, I second the question on installation cost...I'm mechanically inclined, but I've heard that, unless you have experience setting gear preload and/or have someone with experience to babysit you, this really isn't a DIY project... (I should point out that, for me, this would be coupled with a gearing change)