There definitely are trends. I wonder how much is driven by a cool new product, how much is from the model magazines, and how much is from an individual modeler (Furlow for example)
For me, I am a foamer first and a modeler second. I'm far more interest in seeing the real thing than an awesome layout. I definitely love Furlow and John Allen's exaggerations...but I'm probably more influenced by Harry Brunk's UC&N (C&S Clear Creek line in HOn3).
Certainly various eras have very specific followers...such as the 1970s with people whom first took an interest in the 1970s...or started a major layout in the 1970s and don't want to scrap their roster to update or backdate it. That's partially why the poll was not about what you're modeling, but what catches your eye.
How many people, either on here or in the hobby, have ever seen a NKP Hudson? (I presume mostly just those whom click the link in my sig) How many had seen a classic 1870s Baldwin 4-4-0 prior to Spectrum's 1:20.3 option? How many had ever seen what a South Park mogul looked like prior to LGB's mis-painted model of the mid-1980s? Yet, I'm sure that almost everyone on here as seen an SD-70, a GP-38-2, or an autorack. Kind of tough to model something you aren't familiar with. Further, even if you'd seen a picture of a South Park mogul, your experience with it is nothing compared to the sights, sounds, and smells of that SD-45. Certainly that impacts where people start in the hobby, and I'd bet that the work in your first few MRs are also quite influential. So, as you find other things of interest, what does it take for you to switch? Do you chase whatever is being done in the magazines...or stay put with where you started.
Engineer used to be the #1 thing that boys wanted to be when they grew up. What is the break point? The end of the steam era. The general public's interest was dramatically reduced. Still, there are those whom still were/are interested...and go about recreating those experiences...chanson d'enfance. For me, that image of youth is getting up every Saturday as my father worked on the NKP 765, his Pullman lounge car, or his NYC 2600 coach. Naturally, I have drawings of and plans to build that lounge car...even though I don't have any interest in any other cars from the Commodore Vanderbilt. I wouldn't have an interest in trains if it wasn't for the 765...and I can relate with John Allen's scene of lynching the diesel salesman.
I abandoned HOn3 due to the size and the appearance of locomotive running gear. Yet, Sn3 might be a better fit for me than On3. I've certainly been tempted by it...but I am established in On3. Further, the On30 locomotives have made it cheaper and easier to build 1880s On3 equipment. I know that my prototype is perfect for me...the scale is the only doubts I have that it is perfect for me. How many others are out there that sit at this point, and jump because of a new product which makes a different scale/prototype/era irresistible? I'd probably switch if a new Spectrum line in Sn3 was released which would allow me to model the South Park with no more effort than I currently must put into it.
Is On30 a trend or a new frontier? Sure, it has been around, but its popularity is new. Further, it has provided enough of a market for MMI to bring out diecast and RTR On3. This has led to commercial On3 flex track and turnouts. The principle advantage to On30 was (and is) that you didn't have to hand lay the track...and On3 now benefits from this (btw, the new On3 2-8-0s from Accucraft can handle 24" curves). Certainly, On30 has its place long term, but it might again lose out to On3 for modeling mainline 3' gauge trains as HOn30 loses to HOn3. Maybe On30 will continue to grow (I view the cumulative growth of On30 & On3 as being good for On3)...or maybe it will lose ground to some new trend. (all I care is that Bachmann keeps turning out the driver sets and convertible locomotives...how about 37" drivers next?...how about a Mason Bogie?!?!?!)
I better stop...I think I'm rambling and this is getting long.
Perhaps a better thread would be: Have you switched your primary modeling focus? Have you: changed scales, changed eras, or changed prototypes since you ended the hobby? Why? Have you thought about this? If so, what has kept you were you are if you haven't switched. Is there an era you'd prefer to see more modelers actively engaged in it?