The Minoura E-105 is an awesome trainer for mountain bikes. I've used this particular trainer, and I've noticed that there is significantly more resistence than most other trainers. After talking to people at Minoura, they tell me that it is geared more towards mountain bikers, and people who pedal with a slower cadence. The exponential resistence is not there though. It does come with a handlebar mounted resistence unit, so you can adjust it as you ride, but I have not felt this exponential reisistence that they claim. It's not necessesarily a bad thing, it is still a very smooth trainer, and being rim drive, will be the quietest trainer you can possibly find. Seriously, it is super quiet too!
If you are a mountain biker, I would 100% recommend this trainer!