Has there been any research into how to maximize in-game tutorials effectiveness? Any blogs, articles or research papers would be appreciated.
The comments say it all, but ... no, there probably hasn't been much research on it. But, one thing is for sure: in-game, interactive tutorials work better than "read this" tutorials.
This is easy to see in Flash games; you can see the evolution of static screenshots/images linked from the main menu ("Tutorial" button) into in-game tutorials (or tutorial-like levels).
The benefit, obviously, would be seeing things happen and how actions play out, while the game progresses, instead of reading a bunch of instructions before you even have a good idea about how the game will go.
This might be really subjective, but could be used as a reference. From my personal experience, tutorials with lots of text immediately turn off some players (tldr) and then they get frustrated when they can't do something that was explained because they didnt read.
Also do not give all the instructions at the start. Players will not see the relevance of some gameplay aspect and will be confused or forget when they actually need it.
The best tutorials are the one that you do not notice. Integrate into your gameplay/story. Make the tutorials feel like they actually matter in some way (advancing story etc...). Kinda like "learn as you play" kind of experience.
Good luck! :D