Something which has been bugging me is the missleading term dpi. DPI is ONLY a printer term, it means "Dots Per Inch." This is generally far higher than your photo's PPI, or "Pixels Per Inch."
The reason there are two different terms is very simple. Most printers are capable of printing many dots of color per pixel. This creates a much better looking print because it can mix blue and red inks within an individual pixel creating a purlple pixel.
I do hope I can get more people to realize that images are sized in PPI, not DPI. This makes it far less confusing to newbies who go out and buy a 4800dpi printer and try to resize their photos to fit!
I hope I have cleared a little confusion,
PS. Did you know that pixel is an acronym for the two words "Picture Element"?