You have just joined a group and want to upload a bunch of your pictures. Doing it one at a time can be so painful. Here is how to add multiple pictures to a group at once.
1. Log into Flickr
2. Click on Organize link
3. Drag photos you want to add to the group into the Batch Edit part of the screen
4. Click on Send to Group
5. Select the group
6. Press OK and wait.
