Currently PM when I have the 10 photos selected it only adds the info to one of the photos.
In addition I want to note that if your keywords are showing up on only one photo, then this means you are using the Metadata (IPTC) Info feature, when you really want the Metadata (IPTC) Template.
In general:
Metadata (IPTC) Info -- used to edit metadata for
one selected photo. (press the 'i' key)
Metadata (IPTC) Template -- used to add metadata to a
batch of photos. (Mac: command-i, Win: control-i)
If you want to add various metadata to a batch of 10 photos, do this:
1. Select the 10 photos
2. Open the Metadata (IPTC) Template. (On a Mac: command-i, on Windows, control-i)
3. Add metadata to the template
4. Click the button "Apply Template to Selected" and that metadata will be applied to all 10 photos
Note: You can tell the difference between the Metadata Info and Metadata Template by looking at the window title
For more info, you can check out this video:
https://www.youtube.com/watch?v=MokqTQZ1XY4 by Carl Seibert. It is a very helpful introduction.
While using the keywords panel can be very valuable as Kirk has pointed out, if you're a sports photographer adding captions in addition to keywords, then mastering the Metadata (IPTC) Template will make your life so so so so much easier.
Hope this helps,
Mick