Long time lurker first time poster. I only just discovered the Twiddler about 6 weeks ago, and have just put in an order for one today. I thought I would chronicle my experience going from never having heard of the Twiddler to (hopefully) 60 WPM or more, and give other new users some idea about what the learning curve might be.
By way of preparation I read all the documentation, and took a look at the typing tutor, configurator, and forum posts just to get an idea of how things worked and what peoples thoughts were, and to see if the Twiddler was something that I thought would be helpful for me.
Once I decided that it might be something I could use, I looked at the different key layouts that people presented, and while there were a lot of different options and very compelling discussions about the benefits of one over the other, I trimmed the options down to three:
In the end I went with Backspice (Thanks @AlexBravo !). There were a few reasons for this. The first is that Alex is a programmer and uses his Twiddler in almost the exact same way that I will be (MacOs, coding, etc). This means that his layout is the most likely to be optimized for my usage pattern. The second is that Alex is a long time user with a tremendous amount of experience - and he is still extremely active. He continues to tweak and adjust things as improvements come up. And finally, he has a number of MCCs that are based on various n-gram data about the english language, and that seemed like a good set of optimizations to me.
Once I settled on a layout, it was time to start memorizing. In one post ( http://forum.tekgear.com/t/how-fast-are-you-getting/50/17) there was a discussion of "Air-Twiddling". This seemed like a good way to learn so I have memorized each key/MCC combination while "Air-Twiddling". I do most of my practicing while walking or driving (I do street signs and billboards for variety). While I'm sure that I will have to make some adjustments when I get the actual device, I have so far memorized the chords for the full alphabet, all 29 MCCs, and about half of the symbols.
Once I got a good way through the chords and gained some (hypothetical) proficiency I felt that it was time to make the purchase.... and that's where things stand currently.
So now I'm waiting for my twiddler in the mail, and once I get it I will start using the typing tutor to gain real-world proficiency. I'll continue to post my experiences here so other new folks can get a sense of what sort of investment starting from scratch would be.