It's not very often I get excited about a trace mineral, but Boron is an exception. Boron ain't boring - let me tell you. Below I am going to outline one thing after another that boron does that is going to help you in the bedroom, including boosting free testosterone.
First of all, boron is a trace mineral that your body needs and, like magnesium, is used by and positively influences many of your tissues and processes. There is no RDA for boron, but a significant percentage of the population is well below the 3 mg/day threshold that many experts would recommend. In fact, the average is considered to be about 1.5 mg/day.  Here is just a partial list of what boron is known to affect: hormones, inflammation, blood plasma, vitamin D, bone maintenance and cognition/learning.  (NOTE: Tell your woman that there is evidence that boron can help with osteoporosis. )
Boron can also be fickle to get in the diet. Only certain plants contain boron and, unfortunately, things like soil and weather can affect boron content significantly. However, if you are eating one of the healthy, research-backed diets, then it is possible to get upwards of 10 mg/day.  Plant foods, such as lentils, nuts, peanuts, avocado and certain fruits and vegetables, all generally have significant boron content.
Researchers, in the above-mentioned study , decided to give participants boron levels near the upper end of what one can get through diet. They gave 8 healthy volunteers right around middle-age 10 mg of sodium tetraborate - Borax for you old-timers - on a daily basis. The results were remarkable.
Looks at the sex life-boosting properties that Borax exhibited:
1. Free Testosterone. Increased 28%.  (See my link on Free Testosterone for more information.)
2. DHT. Increased (not statistically significantly however).
3. Vitamin D. (not statistically significantly, but boron is a known increaser of Vitamin D)
4. C-Reactive Protein. Statisically significant decrease.
5. TNF-alpha. Statisically significant decrease.
CAUTION: Estradiol. One study in healthy men noted a significant increase in testosterone but also a jump in estradiol: "Plasma estradiol concentrations increased significantly as a result of supplementation (51.9 to 73.9 pmol/L) and there was a trend for plasma testosterone levels to be increased. " 
These five changes are a dream-come-true for us men. Notice the nice boost in free testosterone-to-estrogen ratio - this is going to do nothing but help the sex life of most men. And that's just the beginning of the good news. Other studies have shown that Boron is a huge inflammation fighter. (Some people even take it for arthritis.) However, the one caution is the possible increase in estradiol. If you decide to supplement with Boron, you may want to pull your testeosterone and estradiol before. For more information, see my page on Inexpensive Self-Testing Testosterone Labs and Which Estradiol Test is the Best for Men?
So who cares? Well, anything that fights inflammation, particular TNF-alpha and C-Reactive protein is very likely to improve your artery health, which will in turn improve blood flow, slow arteriosclerosis and do many other things to help you pump out more nitric oxide. Remember that C-Reactive protein is a broad measure of systemic inflammation that is strongly predictive of cardiovascular disease. And TNF-alpha is strongly predictive not only of heart disease, but also erectile dysfunction, diabetes, arthritis and many other nasty conditions. See my link on TNF Inhibitors for more information.
NEWS FLASH: We had a great forum thread on boron and the best form and one regular posted a study using calcium fructoborate to "increase Vitamin D 19.6%, DHEA 56%, and Free Testosterone 29.5%. One male participant had an increase of 50% in testosterone." Hard to argue with that, eh?
CAUTION: Boron is very powerful and little study work has been done to determine the proper dosage, side effects, etc. I personally am waiting a few years before taking this mineral, although I do get a little in my Concentrace Mineral Drops of which I take about 20-40 drops per day at the time of this writing, which is about 0.5-1.0 mg/day, a relatively small amount compared to the studies, which have been generally been on supplementation in the 10 mg/day range.  So my approach is cautious and may have little effect, but my goal is primarily to avoid a deficiency.
1) J Trace Elem Med Biol, 2011 Jan, 25(1):54-8. Epub 2010 Dec 3, "Comparative effects of daily and weekly boron supplementation on plasma steroid hormones and proinflammatory cytokines"
2) Reprod Toxicol, 1997 Jan-Feb, 11(1):123-60, "An assessment of boric acid and borax using the IEHR Evaluative Process for Assessing Human Developmental and Reproductive Toxicity of Agents. Expert Scientific Committee"
6) http://www.bioimmersion.com/docs/fructoborate_monograph.pdf, "Vitamin D/ Steroid Hormone Homeostasis and Calcium Fructoborate Supplementation"
7) Biol Trace Elem Res, 1997 Mar, 56(3):273-86, "The effect of boron supplementation on its urinary excretion and selected cardiovascular risk factors in healthy male subjects"