Gingko Biloba has well-known blood flow increasing properties and it also helps acetylcholine bind to receptors, both of which could be a help with erectile dysfunction. And that appears to be the case, at least according to one older study where about half of patients with erectile dysfunction were helped.
However, I have always been cautious about recommending it, because the studies on its erection-enhancing powers are quite old and it has a number of drug interactions. In addition, there are many other excellent herbs and supplements that can help with erectile dysfunction and so Gingko Biloba simply seemed secondary.
However, one study put Gingko Biloba into prominence for those using antidepressant medications. Antidepressants usage is very widespread, covering probably 10% of the population, and one of the common side effects is erectile dysfunction. The majority of antidepressants are SSRI which boost seratonin levels in the brain. Seratonin is the relaxed, feel good neurotransmitter and, unfortunately, can relax one's sexual response as well.
So many individuals on antidepressants must deal with the unwelcome and discouraging side effect of erectile dysfunction and this is where Gingko Biloba can come to the rescue. One journal reported that 76% of men (and 91% of women) were effectively helped from anti-depressant induced sexual dysfunction by taking Gingko.
Often those with antipressant-indused sexual dysfunction will go to their doctor and try a different medication that is either less effective in treating their depression and/or does not improve their erectile dysfunction. Of course, do not take Gingko until you've talked to your doctor, but it may be a nice to have the best of both worlds: the antidepressant medication of choice and restored sexual function as well.
FEMALE LIBIDO: By the way, consider the remarkable efficacy rate for women: 91%. More females than males are on antidepressants due to their lower seratonin levels and so the sex lives of many couples could possibly be assisted if the woman took Gingko Biloba. One study also showed that Viagra could help women out in this area as well. 
NOTE: SSRI's have been under a lot of heat lately. One recent study of some of the blockbuster drugs in this category (such as Paxil, Effexor and Prozac), found that they are no better than a placebo.  Basically, sugar pills/placebos improved symptoms just as much as the drugs. The study did find a small benefit for severely depressed patients, but for mild to moderate symptoms, there appears to be no significant benefit. Talk to your doctor, of course, and you may want to look at my link on Natural Depression Cures as well.
1) Journal of Marital and Sex Therapy, 1998 Apr-Jun 24 (2):139-143, "Ginkgo Biloba for Antidepressant-Induced Sexual Dysfunction"
2) PLoS Med, 2008, 5(2):e45, "Initial Severity and Antidepressant Benefits: A Meta-Analysis of Data Submitted to the Food and Drug Administration"
3) Psychiatr Serv, Aug 1999, 50:1076-1078, "Sildenafil for Women Patients With Antidepressant-Induced Sexual Dysfunction"