Unfortunately due to work, I've only gotten out one time so far and it was all on hard pack mountain roads. So no, I haven't needed my front locker yet.
But since I travel alone when I get out I want to be fully prepared. The more built my 4Runner is, the more comfortable of me taking new trails. I'm pretty sure you won't get anyone to say they've regretted it.
Think of it this way... I bought a .44 when I came back to Alaska. I didn't buy it to use it every time I saw a moose or a bear, but IF I NEEDED to protect myself I had it ready to use.
Now there's others on here like [MENTION=67615]Dirtco[/MENTION], when he's up in the snow I'm sure it was used quite a bit. I'm seeing a lot of trails and pics in Arizona that I could see the benefit of a front locker.
So evaluate yourself and what you want to do. Have you been in any situation where you wished you had one? What kind of country do you live in? Where do you see yourself in 3 years in regards to your 4Runner?