Nice job on these plugins! However, I had the same problem as john--I had to add the contents of ftplugin/matlab.vim to matchit.vim to make the ftplugin work on one of my systems (linux).
More importantly, though, the mlint integration seems almost useless because you have to scroll through every stupid warning mlint spits out to find the true errors. Is there a way to make it only report things that would actually prevent the program from running? (e.g. missing 'end' statements, unmatched parens, etc)
As others have said, the usability could use some work. I just turned a .mat file into a .arff file using this, but at first, I was entering the data matrix the wrong way (should have used the transpose). When I did this, the program created the Instances object with no errors, and would then throw a cryptic nullpointerexception when I tried to write the arff file. It took half an hour going through the weka source code to figure out what was happening--a range check in your program would have saved me that time.