For what it's worth I've managed to get my old API6 Bot working in the API-NG. It took maybe 15-20 hours of work, spread over a few weeks, to convert it, although this included a fairly major rewrite of the Bot 'engine' itself which not everyone will need.
The key is to download the ready-made class libraries that Betfair provide (in whatever language you use), and some of the example programs that users post on the Betfair API forum that make use of them. Once you can see a few basic functioning scripts up and running you can start to see how it all hangs together, and if you're not planning to change your Bot 'engine' at all you can actually make progress quite quickly once you get to this stage. It's just a case of building familiarity with the new syntax and data structures.
The biggest problem I had is that I use VB which is not one of the class library languages that Betfair work with. I ended up finding someone on the forum who'd run the C++ classes through a VB converter. Without these I'd have been screwed so hats off to you, mate, whoever you are!
