I'd really be interested in seeing the published research. I do however agree with the point that there are too many practitioners and advocates who see microfinance as a panacea - and in many ways it is a radical departure from the way aid has previously been provided as it provides a real potential for being a sustainable way to deliver financial services to the poor.

This being said, it is difficult to isolate the effects of finance - and you can't generalize microfinance globally as it really depends on the local regulatory environment as to how successful it can be. To generalize as the Boston Globe has done is to say that the banking sector in Canada, US, Britain, France, etc. are all the same - when we know (the hard way) they are not. Microfinance - like all finance is a great and important step for businesses (and it's not just credit, but other access to bank accounts,etc that the poor in these countries previously had no access to), but it's just one component to building wealth.

For a broader view of development - I'd point to the world bank's doingbusiness.org study - the latest of which just came out a week or two that looks at all areas of business like how easy it is to legally set up a new business, close an old one down, etc.: http://doingbusiness.org/