I'd guess everyone has run into those little white pouches of silica gel. They are included in the shipping materials with electronics and anything else that could be damaged by too much humidity. This is especially true if the item has been shipped across the ocean, such as, say, guitars and other wood instruments. Oceans air tends to be extremely humid, so manufacturers toss a few gel packs into the shipping box to help prevent the guitar getting too humid, and swelling during the trip across the water. Once the guitar has reached your home, though, it's a different story.
The biggest environmental danger to most wood instruments is a lack of humidity. Guitars (and similar instruments) really like the humidity to be around 60%. The lower that number goes, the drier the air, and the more likely your guitar will get too dry and experience cracks, especially in the top of acoustic guitars.
The best thing to do with those little silica gel packs, once you've gotten your new guitar unpacked, is to throw them away. Toss them. Don't save them they really have no further use.
If you'd like to make sure your guitar is feeling comfy, get a hygrometer, which is a meter that reads humidity. Keep one in your house, or if you really want to keep your axe happy, get one to keep in your guitar case and then keep your guitar in the case. Keeping it in the case will help prevent rapid swings in temperature or humidity, both of which can be damaging to your guitar's health.
40%-60% humidity is your guitar's comfort zone. If your guitar is too dry (below 40%), consider picking up a case humidifier at Backstage Music. A few bucks spent on a hygrometer (also available at Backstage) and a humidifier will always be less expensive than payingto get your guitar cracks repaired.