We just bought a plot, and have the rough layout almost finalized with the architect. I'd also like to hear people's experiences. I have three pieces of information to share so far, from these early stages.
First, our architect is a freelance guy, and from our experience that seems like the way to go - unless we just got really lucky with him. The firms we came across want rich people to pay them huge amounts to design beautiful mansions. Some won't even consider a ~2000sqft single family house project. The freelance guy, on the other hand, works entirely with ordinary houses. It's been a great process so far, with just the right mix of soliciting our input, and presenting useful ideas based on his own creativity and experience.
Second: when looking for builders, many/most of them were in the "custom home" business. This is probably not what you (as a MMM forumgoer) want. Rather, it is for spendy people who want a semi-customized McMansion with zero project management hassle, let alone actual work. These companies charge a huge premium for the "we take care of everything and hand you the keys to a finished product" aspect, and are not willing to work for someone who wants to do any of it themselves. A secondary issue is that they achieve the hassle-freeness by dramatically restricting choice. They typically offer just three options for everything individual thing (floors, counters, etc).
Basically, I get the impression that like >90% of the new home market comprises two segments: people rich or irresponsible enough to spend $800k+ on a no hassle custom house, and giant cookie cutter subdivision wastelands that large developers churn out. The optimal approach, with at least some significant portion done DIY, seems to be a corner case. There is of course the MMM approach of doing even the foundation and framing yourself, but I think that's probably too hardcore for even most people on here.
Finally, about the land itself: as
@Fishindude said, that's the most important part. Unfortunately, just as with buying existing houses, it's a real balancing act, maybe moreso. If a plot is perfect - great location in a great city, nothing weird to make building hard - then there's already a house on it, lol. You should go into the search expecting to live on the outskirts, or accept some other tradeoff. For instance, our otherwise perfect land comes with a covenant with several pages of intense restrictions on what you can build (that were fortunately almost all what we would want anyways).
Good to hear about
@texxan1 's experience - that sounds like what we want to do, but are still a little apprehensive about how much of a mess it might turn into. (We're also intending to do almost all the interior finish/fixture stuff entirely ourselves).