G. Miki Hayden: Either, actually, so long as one is consistent.

Yocheved Golani: Yep, fewer keystrokes is my preference, and again, it is clearly not a typo, considering context.

Dennis McCarthy: All of these terms will be single words in lower case soon enough, so why not go there now?

Charlotte Fox Luttrell: Still a hyphenated word.

Mark H. Bloom: ... as in America Online ...

Amy Goldyn: But a company's computers are on line.

Carrie Garbas: Again, the hyphenation fits with our more traditional corporate style. (We still write per cent in two words.)