There is a theoretical problem of lactic acidosis in patients with impaired kidney function

No, it is current.  They cannot do studies every year for things that have already been proven, would not make sense.  The info is good info.  There are tons and tons of Life Extension followers out there that take Life Extension drugs (Smart Drugs).  Durk and Sandy are still going strong and they take a number of them.  Hydergene is also a favorite of mine.  And, Idebenone is far better than coq10: 

 http://curezone.com/blogs/m.asp?f=1184&i=139

The only side effect I have witnessed in about 10% of my patients is stomach upset and diarrhoea. I've found, however, that almost everyone can build up a tolerance to it. I suggest that my patients start with a low dose, as little as one, or even a half tablet per day for a week or two, and then gradually increase the dose as they develop a tolerance. There is a theoretical problem of lactic acidosis in patients with impaired kidney function, but in practice, I have never seen this, despite monitoring thousands of patients on Metformin. Nevertheless, I believe that anyone with impaired kidney function should take Metformin only under the care of a physician, and should have their blood levels of lactic acid checked periodically.

http://www.antiaging-magazine.com/interviews/interview_1.html

Metformin is chemically very similar to Phenformin, an anti-diabetic drug which was discontinued in the United States by the FDA in 1976. The reason for Phenformin's removal from the market was because of a number of excess deaths in diabetic patients, caused by lactic acidosis. These deaths were invariably due to the continued use of phenformin by diabetics who had compromised kidney or liver function. No deaths were ever reported in patients who had normal kidney and liver function.

Phenformin's removal from the market was greatly lamented by most diabetologists at the time, one of whom once told me, "Phenformin did everything! It lowered blood sugar, lowered insulin, reduced blood cholesterol and triglycerides, stimulated immunity, and even resulted in weight loss!" He blamed the excess deaths associated with phenformin's use on the "stupid docs" who continued to use it in the face of abnormal liver or kidney function. Metformin is similar to phenformin in its beneficial metabolic effects, but it is much safer, in that it has even less propensity to cause lactic acidosis than phenformin.

http://www.antiaging-systems.com/extract/metforminweight.htm