The only thing in terms of trains I've ever pre-ordered so far are the upcoming scale Amfleets and one Viewliner from GGD. I know I'm taking quite a shot with this, but it seems like it's not exactly a shot in the dark when it comes to stuff from Scott. After researching many of his past products and reading up on the forums how good his customer service is, I figured why not pre-order what is one of my favorite passenger cars of all time. I genuinely thought it was worth the risk, especially since his stuff is already very difficult to come by. I collect Williams' Amfleet cars, and I'd like to get the E. Welz versions at some point, but to this day no one else has ever made truly scale-length Amfleet cars in 3-rail. We'll see what Atlas does with the recently acquired tooling, but overall I cannot wait for the GGD Amfleet cars and the Viewliner too.
I think pre-ordering isn't a bad thing at all, but like some of you guys mentioned above it can be a unnecessarily bigger gamble than it needs to be. I generally don't pre-order anything myself, but if I do then my rule is to not pre-order things until I see them in-hand (including on the internet), or if I have a previous version of the product and I already know what it's like in terms of quality. Anything that's new for the first time, like new tooling or new electronics, I will never pre-order because I know there is the potential for things to go south really quickly, and I'd rather have the bugs/issues worked out earlier on before I get a product like that. And again, pre-ordering anything from Scott is a huge exception, because of how rare his stuff is and because according to other people on the forums, he has great customer service. If it were Lionel, MTH, Atlas, etc., then more than likely I won't pre-order anything, until I hear how the item is from other people.