Without having looked at the actual studies in detail, it seems that even several of the "no benefit" studies report multivitamins to be beneficial when one does have an otherwise unhealthy diet.

Wikipedia:

Similarly, a 2006 report for the United States Department of Health and Human Services concluded that "regular supplementation with a single nutrient or a mixture of nutrients for years has no significant benefits in the primary prevention of cancer, cardiovascular disease, cataract, age-related macular degeneration or cognitive decline."[16] However, the report noted that multivitamins have beneficial effects in people with poor nutritional status, vitamin D and calcium can help prevent fractures in older people, and that zinc and antioxidants can help prevent age-related macular degeneration in people at a high risk of developing this disease.

In 2007 the United Kingdom Food Standards Agency published an updated set of recommendations for eating a healthy diet.[17] The recommendations stated that pregnant women should take extra folic acid and iron and that older people might need extra vitamin D and iron. However, the report advised that "Vitamin and mineral supplements are not a replacement for good eating habits" and stated that supplements are unnecessary for healthy adults who eat a balanced diet.

From the cited New York Times article:

But a balanced diet typically provides an adequate level of these nutrients, and today many popular foods are fortified with extra vitamins and minerals. As a result, diseases caused by nutrient deficiency are rare in the United States.

In any event, most major vitamin studies in recent years have focused not on deficiencies but on whether high doses of vitamins can prevent or treat a host of chronic illnesses.

(I'll keep taking my multivitamins, as my diet certainly isn't balanced.)