CompUSA is a chain of retail computer and electronic stores in the United States, and is the largest computer retail chain in North America, and probably the most hated as well.
The company was started in 1984 under the name of "Soft Warehouse" in Dallas, Texas, and the first retail location was opened in 1985. From there, its first "SuperStore" (read: really big store) came in 1988, and not far after the name was changed to "CompUSA", reflecting the founders desire to expand nationally. These plans were well on their way when CompUSA purchased the Computer City chain from Tandy in 1998, but immediately after the entire company was slurped up by Grupo Sanborn's, the giant Mexico-based retail company.
Everyone who has ever shopped here has an opinion about it, one way or the other. A typical cross section would probably say that people with a lot of technical knowledge ("Computer Geeks") find the store to be a hideously painful exercise in IQ decrementing, and most other people find it austere and foreboding. But providing you stay away from actual saleshumans as much as possible, the store is an acceptable place to pick up some blank CD-Rs or a new mouse; the caveat is don't expect them to carry any great selection of "Low-Level" parts like Motherboards or CPUs, and those they have should be expected to be out-of-date and overpriced. Remember, it's a "consumer" computer store, and if you treat it is such, you'll be fine.
CompUSA is also one of the places you can find an Apple Computer store-within-a-store; a section devoted solely to the Macintosh and until the Official Apple Stores are more prolific, these will remain one of the few places to play with the new Mac toys hands-on.