If you're like me, about once a week you type something like
>> grep words
and then wait a few seconds before remembering that you really meant
>> grep words *
>> grep -r words *
If so, do yourself a favor and install ack right now. You'll be glad you did.
Note: ack tries to intelligently search only filetypes that it believes to be text. Unfortunately, its built-in list of extensions for such files is incomplete. For instance, it does not include .rst (ReStructured Text) files. To add more extensions, just create a file ".ackrc" in your home directory and put the following line in it:
Here TYPE is the name of the filetype (anything you want) and .ext is the extension of that filetype. For example:
(in the line above, "type" is preceded by two minus characters. Unfortunately, they look strange in my blog's font).