You mean these?
Ignoring the tragic state of my shop -- they definitely have a place on my MTB. Granted it's a low-end hardtail - something I can beat the life out of on the rocks without throwing thousands of dollars at. But if I do feel like spending the cash on a high-end MTB some day, it will have bar ends. For me, it's the perfect hand position for leaning in on an incline or just taking some impact off my wrists.
I still see them all the time.