In domain nomenclature, number dash number dot coms, like 1-1.com, are collectively referred to as N-N.coms. They have a kind of uniqueness and cool-factor that appeals to computer people with math backgrounds (like myself), web designers, domainers and companies.
There are 100 in total, ranging from 0-0.com to 9-9.com, and all were registered years ago. In addition, some can receive a steady flow of traffic; The intrinsic traffic volume will depend largely upon the popularity of the numeric combination.
The aforementioned and other factors have combined to increase their value over the years. If you're able to find an owner willing to part with one, you can expect prices to begin at $1000 US (if you're lucky) and go much higher, depending on quality.
Although desirable, not a lot of uses have been found for N-N.coms as of yet. If you visit some at random, you'll soon discover that very few have been developed. The majority exist as parked pages or are used to redirect traffic to other sites. In fact, most spend their lives as parking pages before being sold on to the next owner.
As a programmer with an interest in design, I'm hoping to go against the parking trend and actually develop this one. I'm just not quite sure which direction I'll be taking it in, so for now, this place-setter will have to suffice while I have a think about it. :)
By the way, if you're using Windows, this page is best viewed through a Safari Browser with the Quartz Engine running. On a Mac, it shouldn't matter. Under all circumstances, high pixel density (ppi) is preferable. Text-based webpages simply don't look right on any other setup.
This web space has been pieced together from scatch pretty quickly. Over time, I'll endeavour to improve things.