A few new ways to invite people to groups or competitions:

Competitions:
If you create a new competition -- on the invite screen, you're prompted to invite all participants from one of your past competitions, and as of a few days ago, you can also invite all the members from one of the groups you administer. 


Groups:
If you are a group administrator, there are three ways to invite people to your group now (see all three in your group admin pane):
-- Invite existing Walker Tracker members by username
-- Invite non-Walker Tracker members by sending an email (and when they join, they will automatically be added to your group)
-- Invite non-Walker Tracker members by posting/emailing a link (and when they join, they will automatically be added to your group)

These features will be very handy for program administrators, as well as team leaders  / organizers.