A friend of mine just got himself one of those Fat Bikes for winter cycling. Says he loves it. It'd be interesting to try it with a trailer, though.
Zero interest in a fat bike. In fact, my hybrid with non-studded 700x35 tires had way more grip than my MTB.
I don't really have any interest in them either, but he has major vertigo issues, and loves the stability it gives him compared to his MTB with studs. Lot's of hills in between his house and work. I rode it around the parking lot when he got it, but the additional weight and rolling resistance is obvious. Granted, when he switched back in the summer, I imagine he rocked the ride. :-)
Personally, I've got a Specialized RockHopper that I use for my daily commute. Was thinking about looking into a road bike of some kind, but I don't think I've hit the limits with it yet. It seems that every ride to work is the fastest ride so far. The
Power Grips I got have made a huge difference. Almost as good as SPDs, without needing a specific pair of shoes.
I might search about for suggestions once I hit the limits of the bike, but right now,
I am the weakest link. Keep getting better though. Hopefully this month I won't fall out of the habit a couple weeks in like I have for the last two months.