The most common "every day" use of the element boron is in the cleaner known as Borax. This cleaning agent is a simple chemical compound called boric acid. Cheap and relatively nontoxic, it is an excellent antifungal agent and can help around the house with everything from dishes, to bathroom cleaning, to laundry.
Boron is also used to strengthen glassware. The glass material known as Pyrex is resistant to breakage and especially fortified against the damage caused by sudden changes in temperature. A boron additive in the glass makes it into a material known as borosilicate glass. This glass does not expand as much when heated or contract as much when cooled. (In other words, it has a smaller coefficient of thermal expansion). Hence, it will not undergo damaging shape changes if you take it out of a hot oven and place it on a cool countertop, for example. Pyrex and other materials like it are especially important in a laboratory setting, where scientists may need to use extreme temperatures for an experiment.
Boron is an important micronutrient for plants, and hence is a component of many quality fertilizers. It helps the plant grow healthy cell walls, and is necessary in small amounts. However, high concentrations of boron can harm the plant, so it's best to use a commercial fertilizer rather that trying to add boron from another source.
Many different industries rely on boron compounds for making their products. In addition to glassware, some ceramic materials have boron additives in order to improve their properties. Boric acid is also used in the manufacture of some plastic materials, and is a key stock chemical for the textile industry.
A more frivolous use of boron is found in pyrotechnics. The green flames in fireworks are usually created with boron compounds. Although barium also produces a green flame when burned, it is a heavy metal and is highly toxic. Boron is a safe alternative for making the beautiful green color we all love to see.
As a human nutrient, boron is necessary in microquantities, but because so little is needed, it is never necessary to take a boron supplement! You will get all the boron you need from your natural diet. Little is known about exactly why boron is necessary for health.
Not all boron compounds are harmless! Boranes and related compounds such as sodium borohydride are important reagents in organic synthesis. They are used to help create designer molecules like drug compounds, food additives, and coloring agents. However, they are highly reactive and must be handled with care by the synthetic chemists who use them. They are not components of any commercial formulations, just starting materials for making the products. When the drug molecule (for example) is made, the reactive boron compounds have been used up in the process.