How to columnize text with tabs (in vim or on the shell)

Set the tab display size to just larger than your longest field.

# original format
abcdefghijklmnop<Tab>field2
abcdefgh<Tab>field2
abcdefghijkl<Tab>field2
I have spaces!<Tab>field2

In Vim,

:echo len("abcdefghijklmnop") " Reports 16
:set noexpandtab tabstop=17

You can probably condense this to one command, but I don't know how. If you're running a modern Vim, :set list will indicate hard tabs with a fancy character (which you can also configure). Otherwise they'll just show as ^I (not what you want) or whitespace.

# displays like this
abcdefghijklmnop>field2
abcdefgh>        field2
abcdefghijkl>    field2
I have spaces!>  field2

EDIT: An example from a real running vim!

The csv.vim - A Filetype plugin for csv files also supports tab-delimited files, and has :ArrangeColumn and :UnArrangeColumn commands for that.