Hardwood Floors Versus Carpet
Allergies
In trying to pin point why hardwood floors have 
made a great comeback, all one has to do is look within their own home. Carpeting contains an enormous amount of nasty stuff including dust mites that cause the simplest forms of allergies. You may think by calling in the steam vacuum guys the problems will disappear. Unfortunately they are often ground deeper into the bottom of the carpet. After time they fall through carpet and padding and become trapped. Ordinary household vacuums do the same.
Odors
Carpeting often traps unusual odors that even the best cleaning cannot remove. If you're fond of dogs and cats, hairs don't get to be a problem with wood floors as they are easier to clean .
Natural And Not Synthetic
Hardwood floors are natural and more eco friendly compared to rugs that utilize petroleum based products in manufacturing. Moreover, dust mites 
cannot survive on wood floors, but they populate carpeting by the droves. Not only does newer carpet turn off many sensitive to allergies, but some that are severely sensitive cannot live with it.
Hardwood Finishes
For those that may be chemically sensitive, new prefinished floors will off gas to an extent but will dissipate quickly. Some Chinese imports may take longer. Conversely, unfinished products that have been finished on site will also have lingering effects but will be more noticeable if oil based types are used. Natural oil finishes that have become popular in the past few years may prove to be the least troublesome for those sensitive.
Appearances
Wood flooring also has their own unique beauty. Besides being beautiful and hard-wearing, they are environmentally friendly as well. Solid 3/4" products will last a lifetime if proper care is applied. Not one single piece among a few possible thousand (depending on the layout) will be the same.
Hardwood Sells Homes
A sizable portion of the renewed interest has to do with increasing a homes value, which in many cases it will, but depends on other factors as well. Being in the right neighborhood certainly helps resale value. However, if you're on the wrong side of town expect your new investment to be enjoyed by yourself only, but adding wood floors to the home has proven effective in selling a home faster.
Rental Properties
Wood floors are a great choice for rental properties. You don't have to choose the expensive stuff, just something that will serve its purpose and last. 
Prefinished cabin grade products are ideal. They don't carry a warranty, but is your tenant going to be concerned with a few flaws here and there? Ask yourself about a potential renter; will they be more impressed with a wood floor or new carpeting?
Prices for decent prefinished cabin grade products can be found as low as $2.00 a square foot. Let's say you have a rental house that changes tenants every two to three years and you own the property for twenty. In that 20 year period the carpeting may have to be replaced 3 or four times if you're a nice landlord and care about what conditions people live in. Basic carpet and padding can run in the one dollar a square foot range. Add professional installation (because you or I don't know how to install it properly without your tenants tripping over ripples) and you're two to three times the hardwood cost. With hardwood it can be done by many do it yourselfers; at least the more simple types, and no major installation costs are incurred.
Where To Look
Finally, considering wood floors make up a large portion of home improvement expenses, I suggest doing your homework first to learn of all the options available today. Unfortunately your average carpet store and wood floors don't go hand in hand, nor does any big home improvement store. The more uncommon applications and wider variety will only be found with a specialty hardwood flooring retailer.
Image Sources: dustmitespedia.com (dust mites)
