so
1GvG:s/..../g
can replace over an entire buffer
However, suppose I have multiple vim buffers loaded, and I want to do a :s over
Since I can't leave comments, I'll be repeating what Brian said and adding in my 2 cents.
I believe the command you're looking for is:
:bufdo :%s/..../g | :w
Note: This will write each file after the changes are made, so make sure you're ready for this.
If autowrite is on, you should be able to remove the "| :w" at the end of the command.