If you'd like to stay up to date with another users submissions to the community, you can 'follow' them. This means you'll receive an email whenever they post an idea in a challenge that you have access to.

To follow a user, click on their profile image from anywhere in the community (this will appear as a grey people icon if they haven't uploaded an image), then click the Follow button which appears under their username:

To unfollow them, just click the button again.