In a Google Docs Spreadsheet, I would expect this formula:
=ARRAYFORMULA(ROW())
to fill the column like:
[ 1] [ 2] [ 3] [ 4]
You need to specify a cell-range argument for ROW() in order to have more than one value.
Try it this way:
=ARRAYFORMULA(ROW(A1:A10))
This will fill a column with row numbers from 1 to 10.